refactor: verify display handler

[JeyJeyGao]

Refactor:

• move the verify command output related logic to be VerifyHandler

Example:

notation verify notationreg.azurecr.io/hello-world:v1
Warning: Always verify the artifact using digest(@sha256:...) rather than a tag(:v1) because resolved digest may not point to the same signed artifact, as tags are mutable.

Successfully verified signature for notationreg.azurecr.io/hello-world@sha256:d37ada95d47ad12224c205a938129df7a3e52345828b4fa27b03a98825d1e2e7

The artifact was signed with the following user metadata.

KEY   VALUE
foo   bar

Resolve part of #1151

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.27%. Comparing base (80cb6ee) to head (0485b7f).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1167      +/-   ##
==========================================
+ Coverage   74.70%   75.27%   +0.56%     
==========================================
  Files          59       60       +1     
  Lines        3337     3365      +28     
==========================================
+ Hits         2493     2533      +40     
+ Misses        651      640      -11     
+ Partials      193      192       -1     

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[shizhMSFT]

LGTM with suggestions

[shizhMSFT]

LGTM

[Two-Hearts]

LGTM

[shizhMSFT]

LGTM