Introduce dummy storage maintenance delay

This MR aims to bring the --storage-maintenance-delay node option that will allow to configure the storage maintenance (aka store merge / context GC) to be delayed.

This first MR paves the way to the introduction of the actual feature (that aims to allow auto and custom delays), by introducing the disabled mode -- aiming to follow the current behaviour (trigger the merge as soon as a new cycle starts).

Manually testing the MR

Green CI

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