DAC: Introduce `V1` API

Context

Part of #5437 (closed), follows !8750 (merged).

This MR introduces V1 API, with the single "GET v1/page" (former "GET v0/preimage") endpoint for the start.

Closes #5579 (closed).

See !8764 (merged) for the follow-up. !8764 (merged) organizes RPC_server code to reflect API versioning, which would ideally prevent developers breaking backwards compatibility accidentally.

Manually testing the MR

Cli should pass.

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