Chore: Extracted the dns monitor to its own monitor-type

[CommanderStorm]

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Description

This PR lifts the DNS-monitor from the gigantic monitor.js into its own monitor-type

Type of change

• Other

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)

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[CommanderStorm]

I can test more of the monitors' functionality if requested, but given that this is just a code-move, I don't feel that this would be able to uncover any further bugs. (I have not touched the code at all, just where it lives)

Secondary reason:
It is really hard to find example domains to test against 😅

[Computroniks]

Looks good 👍
Slight side note, that massive if else block looks like the perfect candidate for a switch block

[CommanderStorm]

Slight side note, that massive if else block looks like the perfect candidate for a switch block

I limited the refactoring to lifting the code to another place
=> Any adjustments like the ones proposed by #432 / ... can be done afterwards