Improve ntfy notifications

[mtelgkamp]

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Description

Improve ntfy notifications.

• use tags red_circle for down and green_circle for up
• increase priority for down alert by 1 if not already max
• add monitor name and status to title
• use heartbeat msg as Message
• add monitor url as action

Type of change

• Other (improve 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 generate no new warnings
• My code needed automated testing. I have added them (this is optional task)

Screenshots (if any)

[mabed-fr]

Hello

Good job !

Why not replace "keyword" with the word actually searched by the probe/check?

[mtelgkamp]

Good job !

Thank you

Why not replace "keyword" with the word actually searched by the probe/check?

I use the variable heartbeatJSON.msg for the message, so changes to the text are not part of the notification, but need to be done where the variable is filled, to change the text for all notification providers.