Convert PG Composite Types to Tuples in CH

[dungeon-master-666]

Currently custom composite types from postgres are saved as strings in CH which makes it inconvenient to access/filter/sort/etc them. This PR adds functionality converting composite types to Tuple.

1. Nested composite types and arrays of composites are supported
2. Clickhouse doesn't have Nullable(Tuple(...)) so instead every field of tuple is created Nullable (if PEERDB_NULLABLE is enabled)
3. Apparently this feature should be wrapped in setting to make existing mirrors won't break.
4. I tested only the direct scenario, PG -> CH mirror. PG -> PG and others were not tested

[serprex]

#3066 introduced versioning as a simpler alternative to settings for maintaining backwards compatibility

[serprex]

wanted to get to bringing this to a point we can merge, but been falling behind this past month

[dungeon-master-666]

wanted to get to bringing this to a point we can merge, but been falling behind this past month

I'm doing a bit of refactoring right now and fixing several issues. Will be ready for review in a day or 2.

[dungeon-master-666]

Hi @serprex @heavycrystal, it's ready for reviewing. I've added a new version CompositeTypeAsTuple for backward compatibility and fixed several issues with arrays of composites and nested tuples.

[serprex]

this is failing in CI for #3384

failed to fetch custom type mapping: failed to load composite types: Unknown field for composite type "geometry_dump":  field "geom" (OID 18053) is not already registered.

seems like there's a mess with having to make sure dependencies are registered before loading. Looking at LoadTypes this can probably be cleaned up to query catalog ourselves for composite types specifically & figure out how to register types in correct order

[dungeon-master-666]

Weird, LoadTypes already has some logic for registering children types before parents: https://github.com/jackc/pgx/blob/master/derived_types.go#L82-L84