When `disable_overriding_approvers_per_merge_request` is set to
`true`, we must not allow anyone to override the approvers per
merge request.

To ensure this, we shouldn't pass `approval_rules_attributes`
param when creating or updating a merge request whenever it is not
allowed to override the approvers per merge request.

Fix is to add a check to `ApprovalRules::ParamsFilteringService`
to delete the `approval_rules_attributes` from params when it's not
allowed.