Added Pumble Notification

[cs-jako]

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Description

Notification Provider for Pumble (similar to Slack)

Type of change

Please delete any options that are not relevant.

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

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 tested it
• I have commented my code, particularly in hard-to-understand areas (including JSDoc for methods)
• My changes generates no new warnings
• My code needed automated testing. I have added them (this is optional task)

Screenshots

Event	Screenshot
UP
DOWN
Certificate-expiry
Testing

[CommanderStorm]

Overall, this looks good.
I have left a few changes below. Mostly, could you clairify in a helptext where the webhook url can be found.

[cs-jako]

@CommanderStorm I finally had the time to get back to this project. I'm a bit confused about the Review regarding certificate expiry, so I've done some testing. When using expired.badssl.com heartbeatjson and monitorjson are not null and the service is considered as down. This is what I assume is expected behaviour according to the documentation.

I currently have a website where the certificate is about to expire in 21 days, awesome for testing. When adding an alert for that website with certificate expiry alert this is what I get:

MonitorJson
null
-----
HeartbeatJson:
null
-----
Msg: [<monitor_name>][<website>] server certificate <website> will be expired in 21 days

Which would trigger the test alert. But according to the documentation only heartbeatJSON is supposed to be null.
If I'm doing something wrong please let me know, otherwise please advise on how to proceed.

[cs-jako]

^ issue still persists after syncing fork with upstream