Proto: SCORU: add L1 operation for cementing SCORU commitments

Context

See #2119 (closed).

This MR adds a new manager operation Sc_rollup_cement which cements (previously terminology was 'finalizes') a commit in a SCORU. This MR doesn't involve adding any business logic---the new manager operation's application rule simply calls the function in the Sc_rollup_storage module that was added by !4173 (merged).

In this MR there are no new tests because it will be much easier to test the new manager operation once the 'publish commitment' operation is also added (see #2108 (closed)).

Manually testing the MR

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