Add plugin registry

[ffjlabo]

What this PR does:

Why we need it:

Which issue(s) this PR fixes:

Fixes #

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 52.88462% with 49 lines in your changes missing coverage. Please review.

Project coverage is 26.20%. Comparing base (602bf8c) to head (0681f93).

Files with missing lines	Patch %	Lines
pkg/plugin/registry/registry.go	67.74%	20 Missing ⚠️
pkg/app/pipedv1/controller/planner.go	41.66%	10 Missing and 4 partials ⚠️
pkg/app/pipedv1/cmd/piped/piped.go	0.00%	11 Missing ⚠️
pkg/app/pipedv1/controller/controller.go	0.00%	3 Missing ⚠️
pkg/app/pipedv1/controller/scheduler.go	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5466      +/-   ##
==========================================
+ Coverage   26.15%   26.20%   +0.05%     
==========================================
  Files         457      458       +1     
  Lines       49111    49172      +61     
==========================================
+ Hits        12843    12885      +42     
- Misses      35246    35263      +17     
- Partials     1022     1024       +2     

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[ffjlabo]

It's too large, so I will split this PR.