Generate referenced sections list in manual

[lukaseder]

Our manual supports cross references between sections. It would be interesting for each section to have a list at the bottom containing backlinks to all sections referencing it. E.g. the SEEK clause:

• https://www.jooq.org/doc/3.18/manual/sql-building/sql-statements/select-statement/seek-clause/

Is referenced from:

• https://www.jooq.org/doc/3.18/manual/sql-building/sql-statements/select-statement/limit-clause/
• https://www.jooq.org/doc/3.18/manual/sql-building/synthetic-sql-clauses/
• https://www.jooq.org/doc/3.18/manual/sql-building/dsl-context/custom-settings/settings-seek-clause/

[lukaseder]

I'm publishing a draft implementation now. Let's see if this is useful. Some sections will have very long lists of references, in case of which further tuning might be required.

[lukaseder]

This is a great feature in fact! Whenever a Settings section documents the behaviour of a feature, that feature can be referenced, and in turn, automatically has a backlink to the Settings!

Example: #14511