feat: Agent services, refactor generic models

[ondrej-fabry]

• switch from gogo to official proto package: github.com/golang/protobuf
• register grpc server for reflection
• add service subcommand to agentctl
• add service list command for listing services/methods
• add service call command for calling services
• add metrics list command
• add metrics get command
• add Class to model spec
• rename genericmanager to generic
• add generic.MetaService for managing models

[codecov]

Codecov Report

Merging #1494 into dev will increase coverage by 4.09%.
The diff coverage is 32.43%.

@@            Coverage Diff             @@
##              dev    #1494      +/-   ##
==========================================
+ Coverage   51.15%   55.25%   +4.09%     
==========================================
  Files         631      346     -285     
  Lines       78204    29938   -48266     
==========================================
- Hits        40008    16543   -23465     
+ Misses      35768    12103   -23665     
+ Partials     2428     1292    -1136

Flag	Coverage Δ
#e2e1904	?
#e2e1908	?
#unittests	55.25% <32.43%> (+1.09%)	⬆️

[VladoLavor]

Why are netalloc/interface key files (in models) named z_keys.go?

Otherwise looks good.

[ondrej-fabry]

Why are netalloc/interface key files (in models) named z_keys.go?

It was a test with initialization. Will rename back.