spec: add spec for notation version command

[yizha1]

Add spec for notation version command.

[codecov-commenter]

Codecov Report

Merging #376 (5c3b110) into main (6e8e9c5) will increase coverage by 1.49%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #376      +/-   ##
==========================================
+ Coverage   30.54%   32.03%   +1.49%     
==========================================
  Files          25       26       +1     
  Lines        1614     1670      +56     
==========================================
+ Hits          493      535      +42     
- Misses       1108     1122      +14     
  Partials       13       13              

Impacted Files	Coverage Δ
cmd/notation/push.go	21.91% <0.00%> (-2.70%)	⬇️
internal/cmd/flags.go	52.74% <0.00%> (-1.80%)	⬇️
internal/cmd/signer.go	0.00% <0.00%> (ø)
internal/cmd/options.go	0.00% <0.00%> (ø)
cmd/notation/cert_gen.go	0.00% <0.00%> (ø)
internal/envelope/envelope.go	100.00% <0.00%> (ø)
cmd/notation/verify.go	26.89% <0.00%> (+8.26%)	⬆️
cmd/notation/sign.go	42.45% <0.00%> (+12.56%)	⬆️

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[priteshbandi]

Added one feedback. Please incorporate before pushing change.

[shizhMSFT]

LGTM