1. Create a new CommaSeparatedListAttribute class. This is to indicate
   types which are sent to the GitLab server as
   comma-separated-strings (CSV) but we have been allowing users to
   use a list-of-strings.  These values are NOT array values, so
   adding [] to the key name breaks them.

2. Rename ListAttribute to ArrayAttribute.

3. If a value is of type ArrayAttribute then append '[]' to the name
   of the value.

4. Move processing of most GitlabAttributes into the
   client.py:http_request() method. Now we convert our params into a
   list of tuples so that we can have multiple identical keys but with
   different values.

Fixes: #1698

Create return type-hints for `RESTObject.get_id()` and
`RESTObject.encoded_id`. Previously was saying they return Any. Be
more precise in saying they can return either: None, str, or int.

Updated a few remaining usages of `self.id` to use `self.encoded_id`
as for the most part we shouldn't be using `self.id`

There are now only a few (4 lines of code) remaining uses of
`self.id`, most of which seem that they should stay that way.

chore(objects): use `self.encoded_id` where could be a string

Updated a few remaining usages of `self.id` to use `self.encoded_id`
where it could be a string value.

Co-authored-by: John Villalovos <john@sodarock.com>