Resolve ambiguity with apprise.plugins module namespace

While the namespace is physically made of modules, it has been amended
to be the namespace home for the corresponding notifier classes as well.

This turned out to confuse both humans and machines on various ends.

While it has apparently worked for a while, it croaks on Python 3.11
now, and is not considered to have been a good idea in general.

test/test_plugin_pagerduty.py

@@ -22,7 +22,7 @@
 # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 # THE SOFTWARE.
-from apprise import plugins
+from apprise.plugins.NotifyPagerDuty import NotifyPagerDuty
 from helpers import AppriseURLTester
 
 # Disable logging for a cleaner testing output
@@ -61,47 +61,47 @@ apprise_url_tests = (
     }),
     ('pagerduty://myroutekey@myapikey', {
         # minimum requirements met
-        'instance': plugins.NotifyPagerDuty,
+        'instance': NotifyPagerDuty,
 
         # Our expected url(privacy=True) startswith() response:
         'privacy_url': 'pagerduty://****@****/A...e/N...n?',
     }),
     ('pagerduty://myroutekey@myapikey?image=no', {
         # minimum requirements met and disable images
-        'instance': plugins.NotifyPagerDuty,
+        'instance': NotifyPagerDuty,
     }),
     ('pagerduty://myroutekey@myapikey?region=eu', {
         # european region
-        'instance': plugins.NotifyPagerDuty,
+        'instance': NotifyPagerDuty,
     }),
     # Custom values
     ('pagerduty://myroutekey@myapikey?+key=value&+key2=value2', {
         # minimum requirements and support custom key/value pairs
-        'instance': plugins.NotifyPagerDuty,
+        'instance': NotifyPagerDuty,
     }),
     ('pagerduty://myroutekey@myapikey/mysource/mycomponent', {
         # a valid url
-        'instance': plugins.NotifyPagerDuty,
+        'instance': NotifyPagerDuty,
 
         # Our expected url(privacy=True) startswith() response:
         'privacy_url': 'pagerduty://****@****/m...e/m...t?',
     }),
     ('pagerduty://routekey@apikey/ms/mc?group=mygroup&class=myclass', {
         # class/group testing
-        'instance': plugins.NotifyPagerDuty,
+        'instance': NotifyPagerDuty,
     }),
     ('pagerduty://?integrationkey=r&apikey=a&source=s&component=c'
         '&group=g&class=c&image=no&click=http://localhost', {
             # all parameters
-            'instance': plugins.NotifyPagerDuty}),
+            'instance': NotifyPagerDuty}),
     ('pagerduty://somerkey@someapikey/bizzare/code', {
-        'instance': plugins.NotifyPagerDuty,
+        'instance': NotifyPagerDuty,
         # throw a bizzare code forcing us to fail to look it up
         'response': False,
         'requests_response_code': 999,
     }),
     ('pagerduty://myroutekey@myapikey/mysource/mycomponent', {
-        'instance': plugins.NotifyPagerDuty,
+        'instance': NotifyPagerDuty,
         # Throws a series of connection and transfer exceptions when this flag
         # is set and tests that we gracfully handle them
         'test_requests_exceptions': True,