Allow modifying scaling groups in the modify_keypair mutation

### Main idea

[teams](https://teams.microsoft.com/l/message/19:4d7932db9b2c47e8883acfc523c4d3f5@thread.tacv2/1734580744773?tenantId=13c6a44d-9b52-4b9e-aa34-0513ee7131f2&groupId=b1f3bcf4-facf-40d3-94ab-169abb4f0f52&parentMessageId=1734320889419&teamName=customers%20%26%20clients&channelName=42dot&createdTime=1734580744773)

Currently, to set a `scaling_group` for a keypair, we need to use the `associate_scaling_groups_with_keypair` mutation in addition to the `modify_keypair` mutation. This can have unexpected side effects and is not a good practice in terms of error handling.

To address these issues, it is proposed to modify the `modify_keypair` mutation to include the ability to modify `scaling_groups`. This change will streamline the process and improve the overall functionality and reliability of the system.

### Anything else?

Currently, if scaling_groups are assigned to the Keypair, it cannot be reassigned to 'associate_scaling_groups_with_keypair' mutation. For reassignment, we must deallocate through 'disassociate_scaling_groups_with_keypair' mutation and try again with 'associate_scaling_groups_with_keypair' mutation.

And neither both association nor disassociation mutations work with scaling_groups argument of empty strings or empty arrays.

JIRA Issue: BA-7