Remove local maindb driver

[lferran]

Description

We remove the local implementation of the maindb driver for the following reasons:

• We have opted in for pg as maindb since long time ago.
• It has never been production-ready, it has some known bugs and it has been only used for testing so far.
• Right now it's very easy to spin up a local pg instance and make nucliadb depend on it.

This will allow us to:

• Remove the catalog implementation based on the index node.
• Then, we can have shard assignation for resources when ingesting messages coming from processing.
• The above two points allow us to increase/remove the back-pressure mechanism -- we had it in place because we were assigning resources to shards on resource creation, and that, when the ingestion pipeline was too loaded, could make us place way more resources into a shard than we were capable to handle.

How was this PR tested?

Existing tests should cover us. I'm just removing code

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 86.51%. Comparing base (8620248) to head (12e7671).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
nucliadb/src/nucliadb/standalone/config.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2636      +/-   ##
==========================================
+ Coverage   86.19%   86.51%   +0.32%     
==========================================
  Files         377      376       -1     
  Lines       23776    23602     -174     
==========================================
- Hits        20493    20419      -74     
+ Misses       3283     3183     -100     

Flag	Coverage Δ
nucliadb	74.08% <60.00%> (+0.32%)	⬆️
nucliadb-ingest	28.56% <40.00%> (+0.04%)	⬆️
nucliadb-reader	24.55% <40.00%> (+<0.01%)	⬆️
nucliadb-search	37.75% <60.00%> (+0.13%)	⬆️
nucliadb-standalone	46.84% <40.00%> (+0.21%)	⬆️
nucliadb-train	44.96% <40.00%> (+0.21%)	⬆️
nucliadb-writer	39.30% <40.00%> (+0.15%)	⬆️
nucliadb_dataset	55.45% <ø> (ø)
nucliadb_models	84.85% <ø> (ø)
nucliadb_sdk	80.11% <ø> (ø)
nucliadb_sidecar	89.03% <ø> (ø)
nucliadb_telemetry	86.55% <ø> (ø)
nucliadb_utils	84.31% <ø> (ø)

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[jotare]

I think nidx needs v13, maybe we can already use that