Cosign verify updates

Merge Request Description

Related to https://repo1.dso.mil/platform-one/private/big-bang/ironbank/ironbank-bootstrap/-/issues/1316

updates:

• allow for either a public key or certs. (we'll probably never use certs over the public key but we needed it during testing and decided to leave it as it puts this function more inline with the actual cosign cli.)
• use file path instead of string

Merge Request BOE

Risk

Rollback Plan

Testing