chore(test): move pytest cli args definition

The `--broker-url` PyTest CLI argument is used by the examples to
determine whether a Broker is automatically launched, or whether an
existing broker is used.

All PyTest CLI arguments _must_ be defined in the root directory of the
project. As a result, the previous location where these arguments were
defined meant that the examples could only be launched of PyTest was
specifically pointed at the `examples/` directory.

This commit moves the definition to the root directory, thereby unifying
the `examples/` with the remaining tests.

Signed-off-by: JP-Ellis <josh@jpellis.me>

Author: JP-Ellis

conftest.py

@@ -1,8 +1,9 @@
 """
-Global Pytest configuration.
+Global PyTest configuration.
 
-This file is used to define global Pytest configuration. In this case, we use it
-to define additional command line options to customise the examples.
+This file is automatically loaded by PyTest before running any tests and is used
+to define global fixtures and command line options. Command line options can
+only be defined in this file.
 """
 
 import pytest