Improved throughput: reduce unnecessary overload on gRPC bidirectional stream by avoiding empty responses

[rafaeling]

Databroker was underperforming compared to sdv.databroker.v1 APIs implementation.
gRPC bidirectional stream buffer was being overloaded due to the unnecessary return of empty responses, which caused reduced throughput and buffer congestion.

If we accept this change, Provider will fire and forget since Databroker will not send back any ACK message. Could it overload the gRPC buffer?

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 59.36%. Comparing base (e737ae0) to head (40f071c).
Report is 2 commits behind head on feature/databroker-api-v2.

Files with missing lines	Patch %	Lines
databroker/src/grpc/kuksa_val_v2/val.rs	75.00%	2 Missing ⚠️

Additional details and impacted files

@@                    Coverage Diff                     @@
##           feature/databroker-api-v2     #100   +/-   ##
==========================================================
  Coverage                      59.36%   59.36%           
==========================================================
  Files                             33       33           
  Lines                          16005    15998    -7     
==========================================================
- Hits                            9502     9498    -4     
+ Misses                          6503     6500    -3     

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[erikbosch]

Noticed the TODO - Is it so that we currently do not check token, even if broker is configured to require token?
If so, something we better should fix before release - not necessarily part of this PR?

[erikbosch]

But we have let broker = broker.authorized_access(&permissions); earlier, so it is "broker" that does the check on the line below. Could you confirm @argerus

If so just remove the TODO above.