[columnar] Update index whitelist to include GIN and GIST

[JerrySievert]

This PR expands the whitelist for which indexes are allowed to be created against a columnar table.

This does not mean that these indexes will be automatically used, in fact in many cases the indexes will not be used. This just allows for additional indexes to be created which can be used either by explicitly disabling columnar.enable_custom_scan or by using a plan modification such as pg_plan_hint.

Newly supported indexes:

• gin
• gist - also supports postgis indexes and pg_embedding indexes
• spgist
• rum - external gin-like index type

Not supported:

• brin - difficult to support due to how it is tied into the storage
• bloom - supportable, but unable to get the index to be used, so left off white list, might be worth a second look later