Signer/client: introducing versionning of BLS keys

What

This MR introduce a versioning of BLS keys in the client and the signer.

This versioning was already partially supported through protocol client, but not in the protocol agnostic client part. Signer messages have been updated to give the information about the version to use to sign the BLS keys.

The version could still be forced if needed with the TEZOS_SIGNER_SIGNING_VERSION env variable in the client calls are at remote signer launch.

Why

This work is essential for the switch for BLS Aug to Pop in alpha protocol in follow-up MRs.

How

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