builtins: hide multitenancy functions from docs and fix categories

[rafiss]

fixes #84846
fixes #84756

In the public docs, we don't show multitenancy-related functions. This
also fixes the category for sql_liveness_is_alive and row_to_json.

Release note: None

Release justification: docs only change

[cockroach-teamcity]

This change is 

[rafiss]

tftr!

bors r=ecwall

[craig]

Build failed (retrying...):

• Bazel Essential CI (Cockroach)

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

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error creating merge commit from 7921415 to blathers/backport-release-21.2-87132: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 21.2.x failed. See errors above.

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error creating merge commit from 7921415 to blathers/backport-release-22.1-87132: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 22.1.x failed. See errors above.

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