Agnostic_baker: Fix double logging

What

Previously, the mechanism to ensure that we prevent double logging in the agnostic_baker was not entirely correct.

We do not want to close the sinks from the main caller (which is the agnostic baker), but rather to not open new ones from the secondary callers (which are the protocol-dependent bakers). So, now instead of closing the sinks from the agnostic baker when a new baker process is spawned, we now disable the logging for that baker process (via an optional argument, such that the existing protocol-dependent baking binaries are not affected at all). This way, we only maintain the logging from the agnostic baker.

Why

How

Manually testing the MR

This change was observed to be necessary from experimenting with tezt-cloud scenarios, so this work is a pre-requisite for !17069 (merged).

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