BREAKING CHANGE: remove deprecated project.issuesstatistics
in favor of project.issues_statistics

BREAKING CHANGE: python-gitlab will now default to gitlab.com
if no URL is given

fix!: raise error if there is a 301/302 redirection

Before we raised an error if there was a 301, 302 redirect but only
from an http URL to an https URL.  But we didn't raise an error for
any other redirects.

This caused two problems:

  1. PUT requests that are redirected get changed to GET requests
     which don't perform the desired action but raise no error. This
     is because the GET response succeeds but since it wasn't a PUT it
     doesn't update. See issue:
     https://github.com/python-gitlab/python-gitlab/issues/1432
  2. POST requests that are redirected also got changed to GET
     requests. They also caused hard to debug tracebacks for the user.
     See issue:
     https://github.com/python-gitlab/python-gitlab/issues/1477

Correct this by always raising a RedirectError exception and improve
the exception message to let them know what was redirected.

Closes: #1485
Closes: #1432
Closes: #1477

Convert our manager usage to be done via type annotations.

Now to define a manager to be used in a RESTObject subclass can simply
do:
      class ExampleClass(CRUDMixin, RESTObject):
          my_manager: MyManager

Any type-annotation that annotates it to be of type *Manager (with the
exception of RESTManager) will cause the manager to be created on the
object.

The 'managers' are dynamically created. This unfortunately means that
we don't have any type-hints for them and so editors which understand
type-hints won't know that they are valid attributes.

 * Add the type-hints for the managers we define.
 * Add a unit test that makes sure that the type-hints and the
   '_managers' attribute are kept in sync with each other.
 * Add unit test that makes sure specified managers in '_managers'
   have a name ending in 'Managers' to keep with current convention.
 * Make RESTObject._managers always present with a default value of
   None.
 * Fix a type-issue revealed now that mypy knows what the type is

repository_archive() returns 'bytes' not 'str'

https://docs.gitlab.com/ee/api/repositories.html#get-file-archive

Fixes: #1584

`retry_transient_errors` can now be set through the Gitlab instance and global configuration

Documentation for API usage has been updated and missing tests have been added.

Also note what should be changed