Add crosslink and clean up alignment in settings API table

What does this MR do?

While reviewing some docs for another MR, I noticed that we could have a better crosslink for one of the CI/CD settings... but while scanning the table, the "jaggedness" of it made it hard to parse. This does a mild alignment cleanup, not auto-aligning the whole table (as that would add a ton of whitespace), but at least aligns related blocks to make the table easier to work with.

Of course, I also added the crosslink.

To see the light alignment cleanup:

• Before: https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/api/settings.md?plain=1&ref_type=heads#L302
• After: https://gitlab.com/gitlab-org/gitlab/-/blob/f320bfaa6854980ef3e503bda968aca50072cec0/doc/api/settings.md?plain=1#L302

Related issues

Related to !123129 (merged)

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