Add MetadataStore methods to PipedService

[t-kikuc]

What this PR does:

Added the following MetadataStore methods to PipedService:

• Get (of stage/deployment)
• Put (of stage/deployment)
• PutMulti (of stage/deployment)

Why we need it:

Plugins need to Read/Write metadata in Piped-side for the following use cases:

• A. Some data need to be persisted for valid restarting (e.g. Wait beginning time in Wait Stage Plugin)
• B. Some data need to be shared across stages (e.g. Canary resources)

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

All modified and coverable lines are covered by tests ✅

Project coverage is 26.19%. Comparing base (48be6ed) to head (f49df77).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5469   +/-   ##
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  Coverage   26.19%   26.19%           
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  Files         458      458           
  Lines       49169    49169           
=======================================
  Hits        12881    12881           
  Misses      35266    35266           
  Partials     1022     1022           

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[khanhtc1202]

LGTM 👍

[Warashi]

Thank you!
LGTM except one nitpick.

[Warashi]

We don't need success field because we can return error as gRPC error.

[t-kikuc]

@Warashi
Thank you! I fixed it f49df77

[t-kikuc]

@khanhtc1202 Would you please approve again?

[Warashi]

LGTM