Tx_rollup,Node: Apply inboxes on transaction rollup L2 node context

Context

This merge request adds the possibility for the Tx rollup node to interpret inboxes that are posted on the L1 chain and in turn build L2 blocks from them. The L2 blocks are composed of a specific header and a "content" which consists of the content of the inbox itself.

The interpretation (or application) of a message takes an L2 context (the one resulting from the application of the previous message in the inbox, or the one resulting from the application of the previous inbox/L2 block when it is the first) and returns a new L2 context (possibly unchanged if the application fails) and a result.

Each message has the resulting context hash associated to it in the L2 storage, as well as the result.

The rollup node also launches an RPC server to retrieve the contents of blocks or to query the balances of the accounts in the rollup.

• Fixes #2582 (closed)

Manually testing the MR

dune exec tezt/tests/main.exe -- -f tx_rollup_node.ml

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