Implement piped plugin service decrypt secret endpoint

[khanhtc1202]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Part of #4980

Does this PR introduce a user-facing change?:

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[codecov]

Codecov Report

Attention: Patch coverage is 18.30986% with 58 lines in your changes missing coverage. Please review.

Project coverage is 22.45%. Comparing base (1258c8d) to head (0408802).
Report is 23 commits behind head on master.

Files	Patch %	Lines
pkg/app/pipedv1/cmd/piped/grpcapi/plugin_api.go	26.53%	36 Missing ⚠️
pkg/app/pipedv1/cmd/piped/piped.go	0.00%	22 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5019      +/-   ##
==========================================
- Coverage   22.45%   22.45%   -0.01%     
==========================================
  Files         520      521       +1     
  Lines       56852    56919      +67     
==========================================
+ Hits        12766    12779      +13     
- Misses      43060    43114      +54     
  Partials     1026     1026              

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[Warashi]

thank you

[ffjlabo]

🚀