Proper external validator initialization

Context

Improves the init request of the external validator. Before, some parameters were sent to the external validator, in the wild, just after the handshake and the init request was noop. This Mr aims to add parameters to the init request so that the init is actually an init.

Manually testing the MR

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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