Env Events, Notifiers and more

[Theldus]

Description

This PR adds a series of features that I have long wanted to bring to Alertik.

In short:

• Environment Events: Unlike static events, Env Events are very user-friendly and easy to configure, and in a few minutes the user already has something functional.
• Notifiers: In addition to Telegram, Alertik now supports three more Notifiers: Slack, Discord and Teams, as well as four more generic ones via webhook.
• Regex: Alertik finally supports regex and also allows you to use the content of the match group to compose the sending message.