v2: validator support for protoc-gen-validate 0.6.0

[danielhochman]

Ports #417 to the v2 branch.

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[codecov-commenter]

Codecov Report

Merging #418 (d9c094d) into v2 (a79558a) will decrease coverage by 28.02%.
The diff coverage is 39.79%.

@@             Coverage Diff             @@
##               v2     #418       +/-   ##
===========================================
- Coverage   83.58%   55.55%   -28.03%     
===========================================
  Files          30       38        +8     
  Lines         932     1341      +409     
===========================================
- Hits          779      745       -34     
- Misses        114      524      +410     
- Partials       39       72       +33     

Impacted Files	Coverage Δ
chain.go	0.00% <ø> (-90.91%)	⬇️
interceptors/auth/auth.go	100.00% <ø> (ø)
interceptors/auth/metadata.go	100.00% <ø> (ø)
interceptors/ratelimit/ratelimit.go	50.00% <0.00%> (-50.00%)	⬇️
interceptors/tags/fieldextractor.go	13.79% <0.00%> (-71.51%)	⬇️
testing/testpb/interceptor_suite.go	0.00% <0.00%> (ø)
testing/testpb/test.manual_extractfields.pb.go	0.00% <0.00%> (ø)
testing/testpb/test.manual_validator.pb.go	0.00% <0.00%> (ø)
testing/testpb/test.pb.go	36.92% <36.92%> (ø)
interceptors/logging/payload.go	67.18% <42.30%> (-15.43%)	⬇️
... and 49 more

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[danielhochman]

Kicking tests

[johanbrandhorst]

LGTM

[johanbrandhorst]

Thanks for your contribution!