release-25.2: docgen: expose WITH/WITHOUT HOLD syntax in SQL cursor diagram

[blathers-crl]

Backport 1/1 commits from #146458 on behalf of @taroface.

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This PR exposes the WITH HOLD / WITHOUT HOLD syntax in the DECLARE ... CURSOR diagram as follows:

Relates to cockroachdb/docs#19590.

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

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Release justification:

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

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[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