Allow for expansion/collapsing of grammar elements based on grammar file

There’s a need to distinguish between exposing SQL statements in the main SQL Grammar documentation page and the specific SQL statement pages within our documentation page. Some grammar elements have the `/* SKIP DOC */` flag, which skips the statement entirely from both the individual statements and the main grammar file. Having the ability to display one and not the other will grant greater flexibility to writers and engineers.

Kathryn is doing some work to try to expose some cluster virtualization commands, but the general consensus is those commands should not be made available in the main SQL Grammar docs page.

Jira issue: CRDB-31704