add handling of keyless verification for all verify commands

[dmitris]

trafficstars

Summary

Copy the handling of non-Fulcio keys from the verify to all the other verify commands (verify-attestation, verify-blob, verify-blob-attestations).

Currently the large code snippets for the if keylessVerification(c.KeyRef, c.Sk) { code are copied verbatim into several files (yikes!) - the intention is to factor this out into a helper function.

Fix #3759.

Release Note

• add keyless verification and --ca-roots / --ca-intermediates parameters to the verify-attestation, verify-blob, and verify-blob-attestations commands (in addition to verify)

Documentation

TODO - create a corresponding https://github.com/sigstore/docs PR