feat: add gRPC keepalive server parameters

[FerroEduardo]

Reason

Due to the nature of HTTP/2 of keeping persistent connections, the usage of the default gRPC Keepalive parameters may become a problem when dealing with k8s autoscaling. The possibility of setting up MAX_CONNECTION_AGE server parameter also enables others client capabilities, such as gRPC client load balancing (1, 2) (without service mesh, such as Istio).

Description

This PR proposes the addition of configurable gRPC server Keepalive parameters.

As the environment variables and keepalive.ServerParameters struct fields are optional, Deckard's previous behavior will remain the same.

References

• gRPC load balancing
• Default keepalive values: 1, 2
• Lessons learned from running a large gRPC mesh at Datadog

[lucasoares]

There is a test failure, fix it and then lgtm

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.21%. Comparing base (5a2182c) to head (e382b6e).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #52      +/-   ##
==========================================
+ Coverage   82.11%   82.21%   +0.09%     
==========================================
  Files          26       26              
  Lines        3696     3716      +20     
==========================================
+ Hits         3035     3055      +20     
  Misses        519      519              
  Partials      142      142              

Files with missing lines	Coverage Δ
internal/service/deckard_service.go	80.03% <100.00%> (+0.76%)	⬆️