Draft: Tx_rollup: Introduce commitments

**# Context

This is the Merge Request #3.A (see the related document for more information). Changes from !3921 (closed):

• Added storage for: commitments, commitment bonds, frozen tez, prerejections.
• Added a RPC call to retrieve commitments.
• Add a L1 operation to create a commitment
• Add a L1 operation to reject a commitment
• Add a L1 operation to retrieve a commitment bond
• Add a L1 operation for pre-rejection
• Add a block finalization step to manage bonds
• Tests for all of the above
• Docs for the above
• TODO: Make commitments and rejections work with Merkle proofs once Irmin 2.10 is merged.

Manually testing the MR

dune exec tezt/tests/main.exe -- --file tx_rollup.ml
cd src/proto_alpha/lib_protocol/test && dune exec ./main.exe -- test "^tx rollup$"; cd -

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, the Development Version section of CHANGES.md for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR**