feat: default database and collection in MetadataDbClient

[helen-m-lin]

closes #151

Default version is v1, which uses metadata_index/data_assets:

docdb_client = MetadataDbClient(
    host="api.allenneuraldynamics-test.org",
)

v2 uses new metadata_index_v2/data_assets.

docdb_client = MetadataDbClient(
   host="api.allenneuraldynamics-test.org",
   version="v2"
)

[dbirman]

General comment: should we set this up so that it pulls from environment variables but has defaults in place? Like in the QC and metadata portals right now I use

API_GATEWAY_HOST = os.getenv("API_GATEWAY_HOST", "api.allenneuraldynamics-test.org")
DATABASE = os.getenv("DATABASE", "metadata_index")
COLLECTION = os.getenv("COLLECTION", "data_assets")

If we set up some generic env variable names here like "DATA_ACCESS_API_HOST", "_DB", and "_COLLECTION" here then in deployments we would have a no-code way of switching apps between dev/prod just from the aws param store. Same with version, could have a default in place, pull from an env variable when present, and still be user-settable for people who need to set it in their code directly.

[jtyoung84]

We could potentially set something up where it searches for configuration settings in an env file or env vars, but I reckon we can do that in a future PR as a nice-to-have.

[helen-m-lin]

Yeah I agree it could be a useful addition. In the SSH client, we did something like that using pydantic_serttings.EnvSettingsSource. The current client does not use pydantic, so this might be better as part of future issue.

[jtyoung84]

It might be better to remove these comments and just make a note above on how to override the fields if needed.

[helen-m-lin]

Updated