[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:

• [x] #1294
• [ ] #1295
• [x] #1296
• [x] #1299
• [x] #1191
• [x] #1189
• [ ] deislabs/ratify-web#47
• [ ] #1120
• [ ] #1300

Issues that will be addressed by this workstream:

• [x] #1190
• [x] deislabs/ratify#861
• [ ] deislabs/ratify#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) https://github.com/deislabs/ratify/pull/1246