alpha: add `(pre)attestation` in the json operation encoding

Context

This MR add encoding for attestation, preattestation, double_attestation_evidence and double_preattestation_evidence operations using JSON_only encoding. This allows to have both endorsement and attestation as accepted kind by the protocol.

This new encoding can be used by octez-codec to encode JSON operation using the attestation kind as an endorsement operation

Manually testing the MR

This MR adds test for new attestation kinds that checks that the protocol accept this kind in input JSON but still returns JSON with endorsement kinds. To run these tests:

dune exec tezt/tests/main.exe -- encoding protocol attestation -i

Checklist

• n/a Document the interface of any function added or modified (see the coding guidelines)
• n/a 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