chore(kuma-cp) annotate required fields in protos

[bartsmykla]

Summary

These fields will be used to mark fields as required in our docs
when generated

Issues resolved

No issue

Documentation

No documentation changes

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.

[jpeach]

How do we keep this in sync with the actual validation code?

[bartsmykla]

@jpeach without automating generation of validators I don't think it will be easy, so probably currently doing it manually will have to be sufficient, or we have to take time to automate validators

[codecov-commenter]

Codecov Report

Merging #2556 (40189e9) into master (19f4803) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2556      +/-   ##
==========================================
+ Coverage   52.21%   52.23%   +0.02%     
==========================================
  Files         869      869              
  Lines       48565    48565              
==========================================
+ Hits        25357    25367      +10     
+ Misses      21162    21152      -10     
  Partials     2046     2046              

Impacted Files	Coverage Δ
api/mesh/v1alpha1/circuit_breaker.pb.go	46.08% <ø> (ø)
api/mesh/v1alpha1/externalservice.pb.go	53.54% <ø> (ø)
api/mesh/v1alpha1/fault_injection.pb.go	47.29% <ø> (ø)
api/mesh/v1alpha1/health_check.pb.go	30.54% <ø> (ø)
api/mesh/v1alpha1/proxy_template.pb.go	33.37% <ø> (ø)
api/mesh/v1alpha1/rate_limit.pb.go	46.84% <ø> (ø)
api/mesh/v1alpha1/retry.pb.go	33.91% <ø> (ø)
api/mesh/v1alpha1/timeout.pb.go	42.79% <ø> (ø)
api/mesh/v1alpha1/traffic_log.pb.go	53.39% <ø> (ø)
api/mesh/v1alpha1/traffic_permission.pb.go	56.06% <ø> (ø)
... and 8 more

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[jpeach]

@jpeach without automating generation of validators I don't think it will be easy, so probably currently doing it manually will have to be sufficient, or we have to take time to automate validators

Yeh we could look at protoc-gen-validate again I suppose 🤷

[jpeach]

This looks reasonable to me, with the caveat that I didn't double-check everything against the code :)