sign-blob: bundle should work independently and respect --output-certificate and --output-signature

[Dentrax]

Fixes #1821
Fixes #2005

Signed-off-by: Furkan [email protected]

cc @priyawadhwa

Summary

$ COSIGN_EXPERIMENTAL=true ./cosign sign-blob /dev/null --output-certificate foo.pem --output-signature foo.sig --bundle foo.bundle

Bundle wrote in the file foo.bundle
Signature wrote in the file foo.sig
Certificate wrote in the file foo.pem

Ticket Link

Fixes

Release Note

Fixed an issue where --bundle flag does not work independently with `--output-certificate` and `--output-signature` in sign-blob 

[codecov-commenter]

Codecov Report

Merging #2016 (36a4785) into main (76184c4) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #2016      +/-   ##
==========================================
- Coverage   26.16%   26.15%   -0.02%     
==========================================
  Files         127      127              
  Lines        7422     7425       +3     
==========================================
  Hits         1942     1942              
- Misses       5225     5228       +3     
  Partials      255      255              

Impacted Files	Coverage Δ
cmd/cosign/cli/sign/sign_blob.go	0.00% <0.00%> (ø)

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[priyawadhwa]

Thanks for fixing this @Dentrax !