Add support for Google Chat Notifications

[bilipp]

Description

This PR adds support for Google Chat notifications.

Type of change

• New feature (non-breaking change which adds functionality)

Checklist

• My code follows the style guidelines of this project
• I ran ESLint and other linters for modified files
• I have performed a self-review of my own code and test it
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• My code needed automated testing. I have added them (this is optional task)

[BufferOverflowed]

This would be awesome! Is it possible to manually modify/create the files from your PR to add this functionality without waiting for a new release?

[louislam]

Notification provider is not only for up/down notification, so it have to be handled general message case.

[bilipp]

Notification provider is not only for up/down notification, so it have to be handled general message case.

Thanks for the hint! Message now only contains the "Application went down" text if the status is DOWN.