release-24.1: sql: add comment about skipped FKs

[yuzefovich]

Backport 1/1 commits from #155721 on behalf of @yuzefovich.

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We just made a change to include skipped FKs (those that we deemed "irrelevant") in the commented out form. This commit improves that logic by adding a comment for why these FKs are commented out, to reduce possible confusion.

Epic: None
Release note: None

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Release justification: low-risk supportability improvement.

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that it falls into one of the following categories (select one):

• Non-production code changes. Includes test-only changes, build system changes, etc.
• Fixes for serious issues. Defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to.

Add a brief release justification to the PR description explaining your selection.

Also, confirm that the change does not break backward compatibility and complies with all aspects of the backport policy.

All backports must be reviewed by the TL and EM for the owning area.

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[blathers-crl]

❌ PR #155727 does not comply with backport policy

Confidence: high
Explanation: The PR does not explicitly address a critical bug as defined by the published criteria. It introduces a supportability enhancement by adding comments to describe why certain foreign keys (FKs) are skipped during SQL explanations. The change aims to improve the clarity of the output, which falls under supportability improvements but not under the express category of critical bugs required for a backport. Additionally, there is no evidence of a feature flag gating this change. The PR does mention a 'Release justification: low-risk supportability improvement' which allows for a policy exemption but this justification needs to be carefully assessed whether it's sufficient to override other policy criteria.
Recommendation: Add a justification as to why this is a critical bug fix that can be safely backported without a feature flag or reconsider the backport

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}