Fix findings page crash and rule severity correctness

[jowg-amazon]

Description

1. Fixes the findings page crash when a custom rule generated a finding and was deleted.
2. Fixes the correctness of the findings rule severity so that it always shows the highest severity in the table.
3. FIxes the correctness of the correlations findings table in the flyout to show the rule with the highest severity. However, this currently excludes threat intel rules.
   

Issues Resolved

[List any issues this PR will resolve]

Check List

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[AWSHurneyt]

Left a clarification question; but otherwise the changes LGTM. Approving assuming CI passes, and we don't need the null checks I asked about.

[jowg-amazon]

Cypress tests were failing in previous PRs
https://github.com/opensearch-project/security-analytics-dashboards-plugin/actions/runs/10783163154/job/29904504255

[opensearch-trigger-bot]

The backport to 2.13 failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/security-analytics-dashboards-plugin/backport-2.13 2.13
# Navigate to the new working tree
pushd ../.worktrees/security-analytics-dashboards-plugin/backport-2.13
# Create a new branch
git switch --create backport-1160-to-2.13
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 1164b98795c3aa82fbd9bb3ebb94254c627559ed
# Push it to GitHub
git push --set-upstream origin backport-1160-to-2.13
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/security-analytics-dashboards-plugin/backport-2.13

Then, create a pull request where the base branch is 2.13 and the compare/head branch is backport-1160-to-2.13.

[opensearch-trigger-bot]

The backport to 2.14 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/security-analytics-dashboards-plugin/backport-2.14 2.14
# Navigate to the new working tree
pushd ../.worktrees/security-analytics-dashboards-plugin/backport-2.14
# Create a new branch
git switch --create backport-1160-to-2.14
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 1164b98795c3aa82fbd9bb3ebb94254c627559ed
# Push it to GitHub
git push --set-upstream origin backport-1160-to-2.14
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/security-analytics-dashboards-plugin/backport-2.14

Then, create a pull request where the base branch is 2.14 and the compare/head branch is backport-1160-to-2.14.

[opensearch-trigger-bot]

The backport to 2.15 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/security-analytics-dashboards-plugin/backport-2.15 2.15
# Navigate to the new working tree
pushd ../.worktrees/security-analytics-dashboards-plugin/backport-2.15
# Create a new branch
git switch --create backport-1160-to-2.15
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 1164b98795c3aa82fbd9bb3ebb94254c627559ed
# Push it to GitHub
git push --set-upstream origin backport-1160-to-2.15
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/security-analytics-dashboards-plugin/backport-2.15

Then, create a pull request where the base branch is 2.15 and the compare/head branch is backport-1160-to-2.15.

[opensearch-trigger-bot]

The backport to 2.16 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/security-analytics-dashboards-plugin/backport-2.16 2.16
# Navigate to the new working tree
pushd ../.worktrees/security-analytics-dashboards-plugin/backport-2.16
# Create a new branch
git switch --create backport-1160-to-2.16
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 1164b98795c3aa82fbd9bb3ebb94254c627559ed
# Push it to GitHub
git push --set-upstream origin backport-1160-to-2.16
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/security-analytics-dashboards-plugin/backport-2.16

Then, create a pull request where the base branch is 2.16 and the compare/head branch is backport-1160-to-2.16.

[opensearch-trigger-bot]

The backport to 2.17 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/security-analytics-dashboards-plugin/backport-2.17 2.17
# Navigate to the new working tree
pushd ../.worktrees/security-analytics-dashboards-plugin/backport-2.17
# Create a new branch
git switch --create backport-1160-to-2.17
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 1164b98795c3aa82fbd9bb3ebb94254c627559ed
# Push it to GitHub
git push --set-upstream origin backport-1160-to-2.17
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/security-analytics-dashboards-plugin/backport-2.17

Then, create a pull request where the base branch is 2.17 and the compare/head branch is backport-1160-to-2.17.

[AWSHurneyt]

Per offline conversation with @jowg-amazon, backporting this PR to 2.13+.