feat: add inspect blob commands

[rrsemlani]

Adding inspect blob commands.
Spec Pr used for ref: #811

[priteshbandi]

Also as per spec we have a new field called signature envelope type. Please add support for it in both oci and blob inspect command.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 68.68132% with 57 lines in your changes are missing coverage. Please review.

Project coverage is 71.05%. Comparing base (eaa5fb4) to head (3ee161f).
Report is 29 commits behind head on main.

Files	Patch %	Lines
cmd/notation/internal/outputs/inspect.go	70.53%	23 Missing and 10 partials ⚠️
cmd/notation/blob/inspect.go	47.50%	21 Missing ⚠️
cmd/notation/internal/osutil/read.go	86.66%	1 Missing and 1 partial ⚠️
cmd/notation/inspect.go	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #888      +/-   ##
==========================================
+ Coverage   64.93%   71.05%   +6.12%     
==========================================
  Files          45       49       +4     
  Lines        2729     2246     -483     
==========================================
- Hits         1772     1596     -176     
+ Misses        795      453     -342     
- Partials      162      197      +35     

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[Two-Hearts]

This function should be moved into internal/osutil/file.go.
And all public methods (including the ones inside internal) should have a function doc. For this function, that would start with // ReadFile ...

[Two-Hearts]

Same here, function doc is missing. Basically, what does this function do? What are the inputs? What are the outputs?

[Two-Hearts]

This function is called Signatures and returning an array of SignatureOutput, so it seems to be processing multiple signatures. However, from its input sigFile []byte and logic sigEnvelope, err := signature.ParseEnvelope(mediaType, sigFile), it actually can only process one signature per call. Please make sure this is by design.

[Two-Hearts]

Since you are return nil, nil right after this line, toggling this local bool seems redundant?

[Two-Hearts]

I have a use case that the user would like to have an array of SHA256 fingerprints, starting from the leaf cert to the root cert, in the output. For example, if the SHA256 fingerprints for leaf is aaaaa, for intermediate 1 is bbbbb, for intermediate 2 is ccccc, and for root is ddddd. Then when I run notation blob inspect my_sig, I could get an array ["aaaaa", "bbbbb", "ccccc", "ddddd"] from the final output.
The current implementation does not support it, where I have to copy/paste/assemble such an array myself. Can we add a new field to the output to show the array?
/cc: @yizha1 @FeynmanZhou

[Two-Hearts]

Please add corresponding E2E test cases for blob inspect command under test/e2e.