Mutating dictionaries is gross and doesn’t work as you’d expect. Better
to have the function return a new dictionary instead.
Means we can be explicit that `created_by` is one of the allowed params
when updating a service.
To prevent typos and inadvertently updating something we shouldn’t,
this adds some filtering to the update_service method to make sure it
is only allowed to update certain attributes of a service.
The service API client was updating every attribute of a service. Which,
while kinda clunky, is fine…
…until something calling it doesn’t pass in every attribute of the
current service. It was then defaulting optional parameters to `None`.
Which resulted in a bug whereby every time a service was set to live,
its `reply_to_address` and `sms_sender_name` got overwritten to be
empty.
This commit changes the `update` method to only require the service ID,
and pass whatever other named arguments it received straight through to
the API. The API handles partial updates just fine (I think).
