feat: use new verify workflow

[binbin-li]

What?

Use the new verification workflow for the verify command. Therefore, we have to make some updates to support it.

1. Remove all local verification related flags and arguments, including signatures, certs, certFiles, pull, local and mediaType.
2. Add config flag so that users can set up verification plugin configs.
3. Use the new verification workflow.
4. Update the hello-signing.md.

Test

Updated the unit tests.
Command output example:

Signed-off-by: Binbin Li libinbin@microsoft.com

[codecov-commenter]

Codecov Report

Merging #342 (e929ed1) into dev-rc.1 (538b7fc) will increase coverage by 0.88%.
The diff coverage is 16.66%.

@@             Coverage Diff              @@
##           dev-rc.1     #342      +/-   ##
============================================
+ Coverage     30.37%   31.26%   +0.88%     
============================================
  Files            26       26              
  Lines          1758     1705      -53     
============================================
- Hits            534      533       -1     
+ Misses         1207     1155      -52     
  Partials         17       17              

Impacted Files	Coverage Δ
cmd/notation/verify.go	33.96% <16.66%> (+16.03%)	⬆️

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[patrickzheng200]

LGTM