chore(*) remove the ./api/ Go submodule

[jpeach]

Summary

Remove the api submodule.

Full changelog

N/A

Issues resolved

This updates #2200.

Documentation

N/A

Testing

• Unit tests
• E2E tests
• Manual testing on Universal
• Manual testing on Kubernetes

Backwards compatibility

• Add backport-to-stable label if the code is backwards compatible. Otherwise, list breaking changes.

[codecov-commenter]

Codecov Report

Merging #2414 (cb6193e) into master (fa046ac) will increase coverage by 0.16%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2414      +/-   ##
==========================================
+ Coverage   52.43%   52.59%   +0.16%     
==========================================
  Files         875      877       +2     
  Lines       47833    47855      +22     
==========================================
+ Hits        25080    25170      +90     
+ Misses      20715    20638      -77     
- Partials     2038     2047       +9     

Impacted Files	Coverage Δ
api/mesh/v1alpha1/dataplane_helpers.go	80.59% <ø> (+1.68%)	⬆️
pkg/core/resources/store/customizable_store.go	77.77% <0.00%> (-11.12%)	⬇️
pkg/plugins/resources/memory/store.go	77.71% <0.00%> (-4.35%)	⬇️
pkg/core/resources/manager/cache.go	79.22% <0.00%> (-2.60%)	⬇️
api/internal/util/proto/proto.go	70.00% <0.00%> (ø)
api/internal/util/proto/types.go	100.00% <0.00%> (ø)
api/observability/v1/mads.pb.go	35.56% <0.00%> (+1.03%)	⬆️
pkg/mads/v1/client/client.go	43.75% <0.00%> (+2.50%)	⬆️
pkg/kds/client/sink.go	52.27% <0.00%> (+4.54%)	⬆️
... and 6 more

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[lahabana]

LGTM. This is the last submodule isn't it?

[jakubdyszkiewicz]

what about backwards compatibility section? can we backport this? I can't see the label

[jpeach]

Yeh maybe should be backported. Are we definitely OK with removing this module? No use case that needs it?

[austince]

The use case for this would be for implementing the Kuma services via the protos directly, like envoy's go-control-plane, right? I considered this for the Prometheus SD but just went with copying the def instead of adding the dependency since it bundled gRPC, which was not needed.
I think this module would need to be refactored anyway to well support these kinds of use cases, so +1 for dropping is my 2 cents.

[jakubdyszkiewicz]

Exactly, it makes sense only if we manage to extract the module with the API and client. +1 for backporting because I don't think there is a use case of using this module only. Worst case scenario is that we will come back to a separate module.