feat: An initial implementation of Notation CLI Trust Store

[patrickzheng200]

This PR targets the dev-rc.1 branch ONLY.

1. Implemented 'notation cert add', 'notation cert list', 'notation cert show', and 'notation cert delete' commands.
2. Temporarily removed logic of 'notation cert generate-test' as this command needs refactor once we finish trust store and trust policy.
3. Merged new updates by JunJie from the cose branch (i.e. setting up envelope type in config.json).

Signed-off-by: Patrick Zheng patrickzheng@microsoft.com

[codecov-commenter]

Codecov Report

Merging #331 (77d7f19) into dev-rc.1 (6fa490a) will decrease coverage by 1.00%.
The diff coverage is 12.22%.

@@             Coverage Diff              @@
##           dev-rc.1     #331      +/-   ##
============================================
- Coverage     30.07%   29.07%   -1.01%     
============================================
  Files            25       24       -1     
  Lines          1639     1737      +98     
============================================
+ Hits            493      505      +12     
- Misses         1133     1215      +82     
- Partials         13       17       +4     

Impacted Files	Coverage Δ
internal/cmd/flags.go	50.00% <0.00%> (-2.75%)	⬇️
internal/cmd/signer.go	0.00% <0.00%> (ø)
cmd/notation/cert.go	17.53% <11.28%> (-17.76%)	⬇️
pkg/configutil/once.go	100.00% <100.00%> (ø)
cmd/notation/cert_gen.go

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[FeynmanZhou]

If we removed notation cert generate-test in this PR, we need to consider how to create a test cert with Trust Store implementation.