Replace listing namespaces with HEAD requests when scanning

[Tishj]

This PR is an attempt to fix performance issues caused by nested namespaces.

As the title says, it replaces the current logic of running "LoadEntries" when first hitting the schema entry set in a transaction, which does a "list namespaces" request.

The replacement being to instead do a HEAD request to check the existence of the namespace in the lookup.
This is done for both IRCSchemaSet::GetEntry and IRCTableSet::GetEntry

[Tmonster]

Thanks! Looks good, but seems like Polaris is failing? I can imagine it's because they don't support the HEAD request to check if tables exist. Maybe I can take a look using our snowflake catalog

[Tmonster]

So I think for Polaris you need to check for if (response->Success() || response->status == HTTPStatusCode::NoContent_204) {

There seems to be another error though, looking into that

[Tmonster]

The other error is because the httpfs submodule pointer on main does not have the code to create a secret with just a bearer token. Working on that. duckdb/duckdb-httpfs#108 needs to merge, then merge v1.4-andium into main, then update the submodule pointer

[Tmonster]

LGTM now.
@Tishj feel free to look at my last commit, otherwise I think we can merge

[carlopi]

I added myself as reviewer, but that's not really adding much. This seems sound and great to have

[Tmonster]

Awesome to have this in 👍