Tezlink/Node: RPC block info

What

Introduce the block info rpc in the tezlink node

Why

This rpc is quite important for wallet and indexing

How

Reuse the already existing function in tezlink backend to retrieve the tezlink block

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