PATCH: Add REINDEX tag to event triggers

Added my v1 patch to add REINDEX to event triggers.

I originally built this against pg15 but rebased to master for the patch
to hopefully make it easier for maintainers to merge. The rebase was
automatic so it should be easy to include into any recent version. I'd love
for this to land in pg16 if possible.

I added regression tests and they are passing. I also formatted the code
using the project tools. Docs are included too.

A few notes:
1. I tried to not touch the function parameters too much and opted to
create a convenience function that makes it easy to attach index or table
OIDs to the current event trigger list.
2. I made sure both concurrent and regular reindex of index, table,
database work as expected.
3. The ddl end command will make available all indexes that were modified
by the reindex command. This is a large list when you run "reindex
database" but works really well. I debated returning records of the table
or DB that were reindexed but that doesn't really make sense. Returning
each index fits my use case of building an audit record around the index
lifecycle (hence the motivation for the patch).

Thanks for your time,

Garrett Thornburg