Nidx node tests

[javitonino]

Settings changes

• Switch config from envy/serde-with to config-rs. The previous setup was a bit annoying to work with and numeric fields (such as in merge settings) were not working due to Serde flatten softprops/envy#26.
• Put the metadata connection in the settings. This makes it much easier to work with the sqlx::tests because they can create the db pool but don't have access to a db connection string. This way we have a single pool when running all components locally which is a better than starting 5 pools (per component).
• Breaking change: Env variables are now separated by __. This is to better support nested structs with fields with underscore in their names.

Grpc changes

• Expose Grpc servers so they can be started by the test fixture.
• Allow setting a random port for the grpc server (and returning it). This means that starting it is a two step operation (1. reserve and get port, 2. start the serving task). This is wrapped in a GrpcServer struct.

Test changes

• Added a fixture that starts API services in order to test. Still very much WIP, to be extended as we migrate more tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.15%. Comparing base (7066f03) to head (e4fd12a).
Report is 1 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #2602      +/-   ##
==========================================
- Coverage   86.19%   86.15%   -0.04%     
==========================================
  Files         376      376              
  Lines       23580    23580              
==========================================
- Hits        20325    20316       -9     
- Misses       3255     3264       +9     

Flag	Coverage Δ
nucliadb	73.56% <ø> (-0.04%)	⬇️
nucliadb-ingest	28.88% <ø> (ø)
nucliadb-reader	24.90% <ø> (+0.01%)	⬆️
nucliadb-search	37.61% <ø> (ø)
nucliadb-standalone	46.88% <ø> (ø)
nucliadb-train	44.97% <ø> (ø)
nucliadb-writer	39.43% <ø> (ø)
nucliadb_dataset	55.45% <ø> (ø)
nucliadb_models	85.04% <ø> (ø)
nucliadb_sdk	80.11% <ø> (ø)
nucliadb_sidecar	89.03% <ø> (ø)
nucliadb_telemetry	86.55% <ø> (ø)
nucliadb_utils	84.36% <ø> (ø)

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