MIR: Add ways to test rollup locally

Context

Depends on !10087 (closed).

There are two basic ways to try rollup - deploy a rollup node locally (without checking for commitments - but that should be irrelevant to us) and go with special debugger.

Here I handle the former and add a Makefile that hides all the gory details, plus add documentation with instructions and caveats. Mostly followed the official doc; the only detail missing there was how to fetch rollup state (the answer - use undocumented RPC method).

Sending an internal message in real deployment requires more actions than sending an external message, and I do not elaborate on it. If someone deems it should be the primary way of testing, I can elaborate the docs or add something to Makefile in a separate merge request.

Note the next MR that adds testing with debugging.

Manually testing the MR

Follow the instructions in the added document. Send an external message (and/or optionally: internal message) and check that the durable storage is updated.

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