Support digest_function in GrpcStore

[bclark8923]

When using an alternative hash function to the default (sha256), GRPC store doesn't receive which hash function to use.

[MarcusSorealheis]

If you are looking to solve this issue, look into resource_info.rs. It predates our support
for Blake3.

[aleksdmladenovic]

I will work on this issue. cc: @MarcusSorealheis, @allada, @bclark8923.

[aleksdmladenovic]

Hi, @bclark8923.

I looked over details of this issue and I have some things unclear about this issue.

FYI, from this PR, we now detect digest function automatically from the request.

And there is code for GrpcStore receiving digest_function from ActiveOriginContext in grpc_store.rs.

nativelink/nativelink-store/src/grpc_store.rs

Lines 438 to 442 in 8d957a5

	digest_function: ActiveOriginContext::get_value(&ACTIVE_HASHER_FUNC)
	.err_tip(|| "In get_action_from_store")?
	.map_or_else(default_digest_hasher_func, |v| *v)
	.proto_digest_func()
	.into(),

nativelink/nativelink-store/src/grpc_store.rs

Lines 494 to 498 in 8d957a5

	digest_function: ActiveOriginContext::get_value(&ACTIVE_HASHER_FUNC)
	.err_tip(|| "In get_action_from_store")?
	.map_or_else(default_digest_hasher_func, |v| *v)
	.proto_digest_func()
	.into(),

nativelink/nativelink-store/src/grpc_store.rs

Lines 541 to 545 in 8d957a5

	digest_function: ActiveOriginContext::get_value(&ACTIVE_HASHER_FUNC)
	.err_tip(|| "In GrpcStore::has_with_results")?
	.map_or_else(default_digest_hasher_func, |v| *v)
	.proto_digest_func()
	.into(),

And just fyi, while I was trying to evaluate this issue, I found out that there were no test files for testing GrpcStore feature.

Did we omit this for specific purpose or just missing and need to be added later?

And I hope you to make it clear how you caught this issue and how you tested.

Thanks.

cc: @allada, @MarcusSorealheis