Docs: Add CPU usage note for --metrics-per-undefined-host.

[grounded042]

What this PR does / why we need it:

While using --metrics-per-undefined-host=true with high cardinality and high request
rate we have also noticed that CPU usage has increased a noticeable amount. This PR
updates the docs on the flag to mention CPU usage increase as a possible side effect.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• CVE Report (Scanner found CVE and adding report)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation only

Which issue/s this PR fixes

No issue - docs update.

How Has This Been Tested?

CPU usage discovered by running the flag with high cardinality of hostnames and requests.

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have added unit and/or e2e tests to cover my changes.
• All new and existing tests passed.

No tests since it's a doc change.

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I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[Gacko]

/retitle Docs: Add CPU usage note for --metrics-per-undefined-host.
/triage accepted
/kind documentation
/priority backlog
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Gacko, grounded042

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Needs approval from an approver in each of these files:

• docs/OWNERS [Gacko]

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[Gacko]

/cherry-pick release-1.12

[Gacko]

/cherry-pick release-1.11

[k8s-infra-cherrypick-robot]

@Gacko: once the present PR merges, I will cherry-pick it on top of release-1.12 in a new PR and assign it to you.

In response to this:

/cherry-pick release-1.12

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[Gacko]

/cherry-pick release-1.10

[k8s-infra-cherrypick-robot]

@Gacko: once the present PR merges, I will cherry-pick it on top of release-1.11 in a new PR and assign it to you.

In response to this:

/cherry-pick release-1.11

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-infra-cherrypick-robot]

@Gacko: once the present PR merges, I will cherry-pick it on top of release-1.10 in a new PR and assign it to you.

In response to this:

/cherry-pick release-1.10

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-infra-cherrypick-robot]

@Gacko: #12309 failed to apply on top of branch "release-1.10":

Applying: docs: add CPU usage note for --metrics-per-undefined-host
Using index info to reconstruct a base tree...
M	docs/user-guide/monitoring.md
Falling back to patching base and 3-way merge...
Auto-merging docs/user-guide/monitoring.md
CONFLICT (content): Merge conflict in docs/user-guide/monitoring.md
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config advice.mergeConflict false"
Patch failed at 0001 docs: add CPU usage note for --metrics-per-undefined-host

In response to this:

/cherry-pick release-1.10

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-infra-cherrypick-robot]

@Gacko: new pull request created: #12310

In response to this:

/cherry-pick release-1.12

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-infra-cherrypick-robot]

@Gacko: #12309 failed to apply on top of branch "release-1.11":

Applying: docs: add CPU usage note for --metrics-per-undefined-host
Using index info to reconstruct a base tree...
M	docs/user-guide/monitoring.md
Falling back to patching base and 3-way merge...
Auto-merging docs/user-guide/monitoring.md
CONFLICT (content): Merge conflict in docs/user-guide/monitoring.md
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config advice.mergeConflict false"
Patch failed at 0001 docs: add CPU usage note for --metrics-per-undefined-host

In response to this:

/cherry-pick release-1.11

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.