Refactor the plugin SDK to set common fields and configs in a single method

[Warashi]

What this PR does:

• merge setCommonFields and setConfig as setFields
• parse DeployTargets in setFields method and store it as a DeploymentPluginServiceServer.deployTargets

Why we need it:

• I don't want to make/call multiple methods to initialize gRPC server
• resolve TODO: cache the unmarshaled config to avoid unmarshaling it multiple times.

Which issue(s) this PR fixes:

Part of #5530

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 0% with 32 lines in your changes missing coverage. Please review.

Project coverage is 26.54%. Comparing base (a64d83d) to head (f2e1ff1).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/plugin/sdk/deployment.go	0.00%	29 Missing ⚠️
pkg/plugin/sdk/sdk.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5623      +/-   ##
==========================================
- Coverage   26.54%   26.54%   -0.01%     
==========================================
  Files         477      477              
  Lines       50663    50666       +3     
==========================================
  Hits        13450    13450              
- Misses      36150    36153       +3     
  Partials     1063     1063              

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[t-kikuc]

LGTM

[Warashi]

@t-kikuc I merged origin/master. Please re-approve 🙏🏻

[t-kikuc]

Thanks!

[ffjlabo]

LGTM