alpha: introduce attestation encoding in apply_results

Context

This MR add encodings for attestation, preattestation, double_attestation_evidence and double_preattestation_evidence in apply_results operations. Encodings that support old endorsement kinds are tagged as legacy but still set as default until attestation kinds becomes the default one.

This MR partially solves #5358 (closed)

Manually testing the MR

There are no automatic tests in the protocol for apply_results operation encoding yet.

• To manually test this MR, change the encoding used in main.ml by removing _legacy
• Compile
• Launch a sandboxed node and client
• Activate Alpha
• Bake a few blocks
• Run octez-client rpc get /chains/main/blocks/head/operations/0 you will observe that endorsements appears with attestation kind in operation contents.

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)
• n/a 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