release-24.3: sql: add comment about skipped FKs

[yuzefovich]

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

---

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

---

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.}

[blathers-crl]

❌ PR #155728 does not comply with backport policy

Confidence: high
Explanation: The provided pull request does not meet the CockroachDB backport policy as specified. Although the PR includes a 'Release justification' line stating that it's a 'low-risk supportability improvement', the justifications under the policy require fixing a critical bug or introducing a feature flag for new changes. The change description suggests this is merely an enhancement to add comments describing skipped foreign keys (FKs), which does not equate to fixing a critical bug as per the defined criteria (stability/security issue, data corruption/loss, significant performance regressions, incorrect results/suboptimal performance, or production debug enhancements). Further, there is no evidence of a new feature flag being introduced to gate this change. Hence, the PR only adds a supportability enhancement without addressing a critical bug or being gated by a feature flag, which is mandatory for backporting.
Recommendation: Reconsider the backport as it does not meet the required critical bug criteria or feature flag gating. Alternatively, if indeed it's crucial for supportability, ensure that it is properly flagged or justified in line with the backport policy.

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

[cockroach-teamcity]

This change is 

[michae2]

I disagree with blathers. This is extremely low risk, and was specifically asked for by Support after an escalation.