Support of get public key API

### What

Use case: to get the public key of the certificate which can be used for doing standalone crypto signature verification.

Would need extension in key management as well.

### Acceptance Criteria (DoD)

API available that returns public key of the certificate

### How

_No response_

Start by locating the existing key-management API and the certificate handling entry points in the repository. Trace how certificates are exposed today and determine where a public-key accessor belongs. Done means an API returns the certificate's public key for standalone cryptographic signature verification, with the key-management extension covered.

Written by the indexing model from the issue text.