Implement digests route for Incremental Cardano DB in aggregator REST API

[jpraynaud]

Why

We need to make the mapping of the immutable files and their digest accessible to the clients in the aggregator REST API. This will enable the verification of the Incremental Cardano DB in the clients.

What

Create a new /artifact/cardano-database/digests route which serves the digests of all the immutable files.

How

• Create a new ImmutableFileDigestRepository SQLite repository which stores the immutable file digests.
• Create a new implementation of ImmutableFileDigestCacheProvider with the ImmutableFileDigestRepository.
• Use this new implementation in the aggregator only.
• Create a new trait ImmutableFileDigestMapper implemented by ImmutableFileDigestRepository which retrieves the map of already computed immutable files and their digests.
• Create a new /artifact/cardano-database/digests route in the REST API that uses the ImmutableFileDigestMapper to provide the map of computed immutable files and their digests.
• Test the route in the end to end test.
• Update OpenAPI.
• Prepare a migration script to avoid long computations on the aggregator?

Later

• Implement the creation of the digest file and uploaders in the Digest builder