WIP: SCORU, Node: Introduce commitments metrics

Context

Fixes #4295

This merge request introduces commitment metrics for SC rollup node.

It adds:

• last_stored_commitment_level
• last_published_commitment_level
• last_cemented_commitment_level

Manually testing the MR

• Run ./octez-sc-rollup-node-alpha dump-metrics and check for the commitments metrics entry
• Run a sandbox rollup node with metrics-addr :1234
• curl -s http://localhost:1234/metrics |grep commitments

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR