WIP: DAL node: Migrate accepted commitment store to KVS

What

Same as !12807 (merged) with another field (the slot_id -> commitment association in the case of accepted commitments).

Stacked on !12807 (merged).

Why

Another step toward removing the legacy store of the DAL node.

How

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