bug: on unrelated name change, api_key shows plan change for prefect_service_account

[parkedwards]

looks like this is less of a bug (the value doesnt' change), but more a side effect of having the api_key attribute as a Computed read-only property. It will always show as a known after apply state because there is no default value, and we can't use the UseStateForUnknown() planmodifier, as the value will change upon rotation