:sparkles: Add support for Apprise notifications

[BHSPitMonkey]

Description

This PR adds Apprise as a supported notification provider.

Apprise is a popular Python library that exposes the ability to notify using dozens of popular notification and messaging services (and protocols), including Discord, Home Assistant, and MQTT.

Users configure Apprise by specifying a URL which contains details of the service being used and any relevant authentication tokens. Some examples borrowed from their documentation:

• Discord: discord://webhook_id/webhook_token
• Home Assistant: hassio://hostname/accesstoken
• MQTT: mqtt://user@hostname/topic

Has This Been Tested?

I've tested this locally using:

camply test-notifications --notifications apprise 

after configuring a APPRISE_URL in my .camply file (using the interactive configurator).

Apprise URLs take many forms depending on the notification service being used. Refer to the documentation for supported schemes and examples.

Checklist:

• [x] I've read the contributing guidelines of this project
• [x] I've installed and used .pre_commit on all my code
• [x] I have documented my code, particularly in hard-to-understand areas
• [x] I have made any necessary corresponding changes to the documentation

[BHSPitMonkey]

Some additional comments:

• I wasn't sure if adding the new package via [project.optional-dependencies] was the correct call here, but I figured it was safe to follow the example set by the Twilio notifier. Please let me know if there's a better way to go (or change at will)!
• This is my first time working with hatch; Apologies if I've missed a step relating to the addition of the new package.

[juftin]

Nice, this looks very solid. Apprise seems like it'll fit a ton of different notification use cases. I will get a closer look at it later to make sure all the hatch stuff is set up right and the tests are passing. Thank you for the contribution 🏕️

[juftin]

Hey @BHSPitMonkey, hope you don't mind, I squashed your commits into one, and then added a couple commits to resolve the issues. I'm new to hatch as well so it took me a sec.

Changes Made

• Default the environment to Python 3.9 This adds some dependencies that more recent of Python don't need
• Freeze The Unit tests in Time
  • There were some unit tests that broke after May 1st due to some time-based limitations. To prevent this from happening to all of the unit tests I did some time traveling using freezegun.

[juftin]

:tada: This PR is included in version 0.20.0 :tada:

The release is available on GitHub release

Your semantic-release bot :package::rocket:

[BHSPitMonkey]

Apologies for what? Easiest time I've had landing a change in a long time :wink: Thanks for the help!