release-24.1: docgen: update ALTER {INDEX,TABLE} SCATTER diagram

[blathers-crl]

Backport 1/1 commits from #153682 on behalf of @rmloveland.

---

Epic: none
Release note: none
Release justification: non-production code change

Diagram preview image:

---

Release justification:

[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 #153751 is compliant with backport policy

Confidence: high
Backward compatible: true
Explanation: The pull request is compliant with the CockroachDB backport policy regarding non-production code changes. The PR body contains a release justification line stating it's a 'non-production code change', which exempts it from requiring a critical bug justification or feature flag gating under the Backport Policy. Moreover, all changed files are relevant to documentation and code generation tools that are specifically for non-production use. The 'docs/generated/' and 'pkg/cmd/docgen/' paths are associated with documentation generation and do not affect the production codebase.

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

[cockroach-teamcity]

This change is