[EPIC] Improve Cosign Verifier

[akashsinghal]

What would you like to be added?

Cosign verifier is currently limited in its configurability and scenarios it supports.
Work Items:

• Add a new key management resource for certs + key management #1294
• Add keys support to new key management resource #1296
• Migrate Cosign verifier to be built in #1299
• Support Cosign verification with multiple keys  #1191
• Support Cosign verification with RSA key #1189
• Create a walkthrough to setup cosign verifier ratify-web#47
• Document Cosign steps in "Ratify on Azure" ratify-web#72

Issues that will be addressed by this workstream:

• Support for Cosign verification with keys managed in KMS #1190
• Configure cosign public key via CRD #861
• Fix cosign rekor URL default #1164

Anything else you would like to add?

No response

Are you willing to submit PRs to contribute to this feature?

• Yes, I am willing to implement it.

[sajayantony]

Thanks for taking the lead on cosign @akashsinghal

[akashsinghal]

Here is the accompanying design discussion document PR encompassing these changes (and more) #1246