Add function to extract anchor data from certificate

[palas]

Changelog

- description: |
    - Add function to extract anchor data from a certificate
  type:
  - feature

Context

This PR is part of addressing this review comment. It moves the extracting of anchor data into cardano-api together with the rest of code that inspects certificates for easier maintenance.

Related PRs

• [cardano-cli] https://github.com/IntersectMBO/cardano-cli/pull/951
• [cardano-node] https://github.com/IntersectMBO/cardano-node/pull/6023

How to trust this PR

It is quite analogous to filterUnRegDRepCreds, except it does some conversion from PoolMetadata to AnchorData which are analogous types.

Checklist

• [x] Commit sequence broadly makes sense and commits have useful messages
• [x] New tests are added if needed and existing tests are updated. See Running tests for more details
• [x] Self-reviewed the diff