Support digest function in GrpcStore

[asr2003]

Description

• Updated ResourceInfo to default digest_function to sha256 if not provided.
• Ensured backward compatibility for existing functionality.

Fixes #1325
/claim #1325

Type of change

Please delete options that aren't relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please also list any relevant details for your test configuration
Tests added

Checklist

• [] Updated documentation if needed
• Tests added/amended
• bazel test //... passes locally
• PR is contained in a single commit, using git amend see some docs

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This change is 

[MarcusSorealheis]

Please do not open up PRs that do not adhere to the checklist, unless they do not impact NativeLink.

[asr2003]

The failed check before isn't known what it is failed for seems a deployment failure! Hopefully the deployments succeeded now

[aaronmondal]

+@allada @MarcusSorealheis What do we do about test coverage here? The grpcStore currently has no tests 😅 https://tracemachina.github.io/nativelink/coverage/build/source/nativelink-store/src/grpc_store.rs.html

@asr2003 I think it should be fine if we just cover the changed parts, i.e. unit tests for the read, has_with_results and is_supported_digest_function, and only tests that trigger the branches that you added (i.e. tests that force the new error handling and check that they're actually hit).

Reviewable status: 0 of 2 LGTMs obtained, and 0 of 2 files reviewed (waiting on @allada)

[asr2003]

Sure! I will add tests to ensure the branch coverage.

[asr2003]

@aaronmondal @MarcusSorealheis @allada Any update on this?

[laz-001]

@aaronmondal @MarcusSorealheis @allada - is this expeted to go through? Otherwise may extend the bounty with the testing-extension?

[asr2003]

@aaronmondal @MarcusSorealheis I have added unit tests as per review comments for the logic added of digests in grpc_store. Can you have a review on this?

[asr2003]

@MarcusSorealheis @aaronmondal Would appreciate your review when you have time.