Backport of Docs/igw docs day refactor into release/1.15.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #17259 to be assessed for backporting due to the inclusion of the label backport/1.15.

🚨

Warning automatic cherry-pick of commits failed. If the first commit failed,
you will see a blank no-op commit below. If at least one commit succeeded, you
will see the cherry-picked commits up to, not including, the commit where
the merge conflict occurred.

The person who merged in the original PR is:
@trujillo-adam
This person should manually cherry-pick the original PR into a new backport PR,
and close this one when the manual backport PR is merged in.

merge conflict error: unable to process merge commit: "2e02a78f3af57ec3cd5b76f16b4166ce4f0d92c0", automatic backport requires rebase workflow

The below text is copied from the body of the original PR.

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Description

This PR refactors the existing ingress gateway documentation into overview, usage, and configuration reference content types. We edited some content for clarity and so that it fit into the content type paradigm, but it is mostly unchanged. Please review for accuracy.

Preview pages:

• Overview
• Main usage page
• Secondary usage page: For this page, please verify the order of the steps. It follows the order of the existing page, but a few questions emerged as we created the draft. Additionally, please verify the description under the 'Configure static SDS clusters' step.
• Configuration reference

PR Checklist

• updated test coverage
• external facing docs updated
• appropriate backport labels added
• not a security concern

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Overview of commits

• 0afff9e - fe56513 - 49a4951 - 1995a5f - 1f39bdf - 5a2e89f - 2e02a78 - 6791fe4 - c551dbe - 59954e7 - 59a1674 - 2a08053 - f590542

[github-team-consul-core-pr-approver]

Auto approved Consul Bot automated PR