MetadataDbClient default database and collection based on version

[helen-m-lin]

Is your feature request related to a problem? Please describe.
Currently users need to know the database and collection names to access the metadata docdb collection. There will now be multiple collections, based on version #. To make it easier for the user, we would like to set the default database and collection names based on the version.

Describe the solution you'd like

• aind-data-access-api sets default database and collection names based on version.
• Lambda function uses version to determine metadata_index database:
  • If v1, use original metadata_index/data_assets collection
  • If v2, use new metadata_index_v2/data_assets collection

Describe alternatives you've considered
Alternatively, the database/collection can be fully handled in the client rather than api gateway

Additional context
Add any other context or screenshots about the feature request here.