Proto: Scoru: add missing protocol constants

Context

closes #2548 (closed) - adding four new protocol constants:

• sc_rollup_stake_amount_in_mutez
• sc_rollup_commitment_storage_size_in_bytes
• sc_rollup_commitment_frequency_in_blocks (replacing hardcoded value in sc_rollup_storage)
• sc_rollup_max_lookahead_in_blocks (replacing hardcoded value in sc_rollup_storage)

and adding tests to ensure that the correct invariants are upheld:

• challenge_window_in_blocks < max_lookahead
• commitment_storage_cost*(max_lookahead/commitment_frequency) < stake_amount

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