feat: support grpc-gateway

[sysulq]

Describe what this PR does / why we need it

Does this pull request fix one issue?

Describe how you did it

Describe how to verify it

Special notes for reviews

[codecov-commenter]

Codecov Report

Merging #405 (579db78) into master (4f8bd4e) will increase coverage by 0.11%.
The diff coverage is n/a.

❗ Current head 579db78 differs from pull request most recent head 960c423. Consider uploading reports for the commit 960c423 to get more accurate results

@@            Coverage Diff             @@
##           master     #405      +/-   ##
==========================================
+ Coverage   52.01%   52.12%   +0.11%     
==========================================
  Files         105      105              
  Lines        6973     6973              
==========================================
+ Hits         3627     3635       +8     
+ Misses       3080     3071       -9     
- Partials      266      267       +1     

Impacted Files	Coverage Δ
pkg/registry/etcdv3/registry.go	74.22% <0.00%> (+2.74%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[stale]

This pull request has been marked as stale due to 60 days of inactivity. It will be closed in 4 weeks if no further activity occurs. If you think that's incorrect or this pull request should instead be reviewed, please simply write any comment. Even if closed, you can still revive the PR at any time. Thank you for your contributions.

[stale]

This pull request/issue is no longer marked as stale.