add grpc reflection

[kpango]

Signed-off-by: kpango kpango@vdaas.org

Description:

support grpc reflection protocols for Vald
https://github.com/grpc/grpc/blob/master/doc/server-reflection.md

Related Issue:

How Has This Been Tested?:

Environment:

• Go Version: 1.16
• Docker Version: 19.03.8
• Kubernetes Version: 1.18.2
• NGT Version: 1.12.3

Types of changes:

• Bug fix [type/bug]
• New feature [type/feature]
• Add tests [type/test]
• Security related changes [type/security]
• Add documents [type/documentation]
• Refactoring [type/refactoring]
• Update dependencies [type/dependency]
• Update benchmarks and performances [type/bench]
• Update CI [type/ci]

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?

Checklist:

• I have read the CONTRIBUTING document.
• I have checked open Pull Requests for the similar feature or fixes?
• I have added tests and benchmarks to cover my changes.
• I have ensured all new and existing tests passed.
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation accordingly.

[vdaas-ci]

[CHATOPS:HELP] ChatOps commands.

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[vdaas-ci]

[WARNING:INTCFG] Changes in interal/config may require you to change Helm charts. Please check.

[codecov]

Codecov Report

Merging #1064 (eb5fa3a) into master (972f77d) will increase coverage by 0.57%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master    #1064      +/-   ##
==========================================
+ Coverage   14.42%   15.00%   +0.57%     
==========================================
  Files         495      498       +3     
  Lines       28408    28770     +362     
==========================================
+ Hits         4098     4317     +219     
- Misses      24054    24178     +124     
- Partials      256      275      +19     

Impacted Files	Coverage Δ
internal/config/server.go	0.00% <0.00%> (ø)
internal/servers/server/option.go	92.19% <100.00%> (+0.07%)	⬆️
internal/servers/server/server.go	69.65% <100.00%> (ø)
internal/db/storage/blob/s3/reader/reader.go	63.04% <0.00%> (-31.53%)	⬇️
internal/errgroup/group.go	92.42% <0.00%> (-1.52%)	⬇️
internal/worker/worker.go	83.33% <0.00%> (ø)
internal/net/option.go	89.65% <0.00%> (ø)
internal/net/dialer.go	79.42% <0.00%> (ø)
internal/net/net.go	45.90% <0.00%> (ø)

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