feat: blob sign command

[Two-Hearts]

This PR adds notation blob sign command with E2E tests.

It's an implementation of spec: https://github.com/notaryproject/notation/blob/main/specs/commandline/blob.md#notation-blob-sign

[codecov]

Codecov Report

Attention: Patch coverage is 90.95477% with 18 lines in your changes missing coverage. Please review.

Project coverage is 72.50%. Comparing base (cb10be5) to head (752afe6).

Files with missing lines	Patch %	Lines
cmd/notation/blob/sign.go	90.05%	14 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1128      +/-   ##
==========================================
+ Coverage   70.79%   72.50%   +1.70%     
==========================================
  Files          48       50       +2     
  Lines        2945     3139     +194     
==========================================
+ Hits         2085     2276     +191     
- Misses        668      670       +2     
- Partials      192      193       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.