doc: add more pages on the DAL

Context

This MR adds more pages in the documentation for the DAL. Before doing so:

• it splits the current DAL page in several sub-pages
• it adds new pages, namely:
  • on the DAL node
  • for the bakers using the DAL
  • on the protocol support for the DAL

Manually testing the MR

Check the accuracy, readability, and rendering of the cover page of the DAL and its subpages, especially the newly added ones.

Checklist

• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR