Plugin: the run_operation RPC does not skip signature checks for non-manager operations

When the run_operation RPC is called on a non-manager operation that has a signature, this signature is checked. This contradicts the description of the RPC, which states that signature checks are skipped.

Since the RPC does not support consensus operations, this affects the voting operations: proposals and ballot.

This issue should be solved once:

• run_operation is refactored to directly call Validate_operation.validate_operation, which will have a new should_check_signature argument (done in !5770 (merged))

• validate_operation is implemented for voting operations (done in !5828 (merged))

Reminder:

• Once this issue is fixed, the parameter sign_correctly can be removed in tezt/lib_tezos/operation_core.ml/make_run_operation_input (also done in !5828 (merged)).