Move all queries on metadata to DuckLakeMetadataManager

[qsliu2017]

I'm working on integrating ducklake with embed duckdb, e.g. pg_duckdb. This PR might be helpful to implement custom metadata manager.

Specifically, this PR:

1. move all queries on metadata to DuckLakeMetadataManager::Query, so that custom implementation can override it to handle metadata queries.
2. DuckLakeTransaction::Query only process queries on duckdb.

[pdet]

Hi @qsliu2017, thanks for the PR!
I’m a bit confused about why you wouldn’t need to replace these query variables if you were going to integrate with a different catalog. Can you expand on that?

[qsliu2017]

why you wouldn’t need to replace these query variables if you were going to integrate with a different catalog.

Do you mean StringUtil::Replace(query, "{METADATA_CATALOG_NAME_LITERAL}", catalog_literal);? They've been moved to DuckLakeMetadataManager.

In my implementation, queries on metadata will not go through DuckLakeTransaction::Query, so it's better that we replace catalog related variables here.