feat: Create module to support library-specific enumeration types

Motivation:

We never know when we might be implementing or extending the
`django-push-notifications` library beyond its current support.

It makes sense to have a module to handle critical moments such as
that raised in #708 (for  `interruption-levels`). This gives control
over newly  implemented interfaces without having to worry about
outdated modules, such as `PyAPNS2`.

This allows us to provide wrapper or extend existing library
functionalities.

Context:

This patch address one side of issue by providing an enumeration module
that can be used to deal with public and underlying APIs.

push_notifications/enums.py

@@ -0,0 +1,37 @@
+"""
+Enumeration Types for public-facing interfaces.
+
+This module contains enumeration types that are used in public-facing and underlying interfaces of the package -
+such as the `InterruptionLevel` of Apple's User Notification System and others.
+
+Created: 2024-03-27 14:13
+"""
+
+from enum import Enum, StrEnum
+
+
+class InterruptionLevel(Enum):
+    """
+    Enumeration of the interruption levels of Apple's User Notification System.
+
+    The interruption levels are used to determine the priority of a notification and the way (delivery timing) it is displayed to the user.
+
+        Ref: https://developer.apple.com/documentation/usernotifications/unnotificationinterruptionlevel
+    """
+
+    # The notification is displayed as an alert.
+    ACTIVE = 0
+
+    # The notification is displayed as a time-sensitive alert.
+    #
+    # Time-sensitive alerts are displayed immediately,
+    # even when the device is in Do Not Disturb mode or the notification is set to be delivered silently.
+    TIME_SENSITIVE = 1
+
+    # The notification is displayed as a critical alert.
+    # Bypasses the Do Not Disturb mode and the silent mode to deliver the notification.
+    CRITICAL_ALERT = 2
+
+    # The notification is displayed as a passive notification.
+    # Pushes the notification to the Notification Center (or list), essentially making it a silent notification.
+    PASSIVE = 3