Crypto: BLS aggregate_signature_opt takes a subgroup_check optional argument

What

Bls.aggregate_signature_opt now takes an optional ?(subgroup_check = true) argument.

Why

In some contexts where the signature subgroup has already been verified, you may want an aggregation function that skips this verification for better perfomances.

How

Slightly updated all previous environments aggregate_signature_opt implementation accordingly so that their version of aggregate_signature_opt remains unchanged.

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.
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