Etherlink/Kernel/Stage 2: reboot between blocks

What

Add a reboot between the application of blocks in the Etherlink kernel.

Why

When lots of blueprints are pending in the storage, as is currently happening on the testnet because the L1 chain stopped for a long time, executing a L1 level takes too much time. Adding reboots between L2 blocks spreads the catch upon several L1 levels.

It also opens the possibility to simplify the block production logic by factorizing the BIP-in-storage and the BIP-from-stored-blueprint cases.

How

Manually testing the MR

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