Agnostic baker starts on known proto

This MR introduces a daemon that monitors node heads so that a protocol is started only when it is assumed to be active.

For example, starting the agnostic baker on a sandbox node before the activation of alpha will result in a waiting phase. As soon as alpha (or any active protocol) is activated, the associated baker binary is launched.

Manually testing the MR

You can try to run the agnostic baker, with the baker arguments, in sandbox. This is not expected to be feature complete.

As the octez-agnostic-baker binary is unreleased, you must compile it with: dune build src/bin_agnostic_baker/main_agnostic_baker.exe && cp _build/default/src/bin_agnostic_baker/main_agnostic_baker.exe octez-agnostic-baker

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