kernel/sequencer: add message to the delayed inbox

Context

When a user sends a message to the kernel, the message should be added to the delayed inbox.

This MR implements a queue that represents the delayed inbox. Then messages from the user are added inside this queue.

Manually testing the MR

$ cd src/kernel_sequencer
$ make test

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