refactor common code from http and grpc subsystem into a service

[huesflash]

Pros:

• This will help keep common code in one place
• flexibility for wrapping service code with various frameworks (ex: gin, fiber)
• existing api is maintained

Cons:

• some extra copies for translating protbufs into request arguments
• naming isn't great

[codecov]

Codecov Report

Merging #82 (c12c453) into main (6695ab3) will decrease coverage by 0.48%.
The diff coverage is 81.63%.

@@            Coverage Diff             @@
##             main      #82      +/-   ##
==========================================
- Coverage   67.87%   67.39%   -0.48%     
==========================================
  Files          54       55       +1     
  Lines        5892     5824      -68     
==========================================
- Hits         3999     3925      -74     
- Misses       1613     1616       +3     
- Partials      280      283       +3     

Files	Coverage Δ
internal/app/subsystems/api/http/http.go	87.17% <100.00%> (+0.90%)	⬆️
internal/app/subsystems/api/http/promise.go	29.92% <67.50%> (-34.60%)	⬇️
internal/app/subsystems/api/grpc/grpc.go	80.21% <75.25%> (-3.55%)	⬇️
internal/app/subsystems/api/service/service.go	87.31% <87.31%> (ø)

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[dfarr]

🎉 🎉 Thank you so much @huesflash, your PR is the first open contribution to resonate!!!

I love the idea to factor out the common code into a delegated service. It also makes a lot of sense if (when) we decide to support additional protocols.

[huesflash]

Added the missing service test!
Should help with coverage as well

[dfarr]

Thank you @huesflash !