Add a generic app service to run an async function as a service

[spencewenski]

Closes #189

[codecov]

Codecov Report

Attention: Patch coverage is 62.83784% with 55 lines in your changes missing coverage. Please review.

Project coverage is 45.36%. Comparing base (b0f89fe) to head (e899d2d).

Files	Coverage Δ
src/service/mod.rs	40.00% <ø> (-13.85%)	⬇️
src/service/registry.rs	98.24% <96.00%> (+0.32%)	⬆️
src/service/grpc/service.rs	0.00% <0.00%> (ø)
src/service/worker/sidekiq/service.rs	33.87% <83.33%> (-3.06%)	⬇️
src/service/worker/sidekiq/builder.rs	55.00% <16.66%> (-0.86%)	⬇️
src/service/http/builder.rs	28.57% <0.00%> (-1.06%)	⬇️
src/service/http/service.rs	19.75% <0.00%> (-0.76%)	⬇️
src/service/function/service.rs	61.53% <61.53%> (ø)

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