Thruk: add disabled_backends field to filter out thruk backends (#219)

[fermino]

This adds support for the feature asked in #219.

[fermino]

@HenriWahl I will need some feedback/advice as how to lay out the GUI elements (I hacked it together but pretty sure it could be better). Let me know if there's anything I can improve!

PS: Thanks for maintaining this project :)

[HenriWahl]

I fixed the GUI a little - the result should be available soon at https://github.com/HenriWahl/Nagstamon/releases/tag/latest with release 3.13-20231130

[fermino]

@HenriWahl thank you!!

[fermino]

Sorry @HenriWahl wouldn't be necessary to merge thruk_backend into master? Do you want me to modify or test anything?

[HenriWahl]

Please test it and if it looks OK it will get into master.

[fermino]

@HenriWahl that definitely looks better. I would just make the label Disabled backends (comma separated IDs) or something similar, as it might not be that intuitive to use. Otherwise it looks great!

[HenriWahl]

@fermino to avoid such a big label maybe just put that information into a tooltip which pops up at the textfield?

[fermino]

@HenriWahl I though about it but I didn't know if it was possible, that would be great!