Crypto: plug signature v2 in environment V15

What

This MR depends on !16986 (merged).

This MR switch the signature version in the environment 15 from version 1 to version 2. It also switches the default signature scheme of BLS keys from Augmented to Proof of Possession

Why

We need BLS signature to use Proof of Possession cryptographic scheme for it aggregation properties.

How

Previous MR:

• create a new signature version
• handle this new version in octez codebase

This MR

• Set this version in the latest env
• Update BLS implementation to use PoP by default (Aug should still be accessible for older protocol)

Manually testing the MR

Green CI for now, A set of additional tests will come later.

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