Add the status of the last run to the tray icon

[Koenvh1]

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Is your feature request related to a problem? Please describe. I run Backrest on my desktop (and it is great, thank you for that!). Sometimes backups fail, generally because I did something stupid. I do have monitoring, but that tells me about it after several days (as I don't want false positives due to me not turning my PC on for a day). Every once in a while, I also manually check whether my backups succeeded.

Describe the solution you'd like Before Backrest, I used Duplicati. Duplicati would change the tray icon based on what the status of the current backup run (an arrow for still running, a red cross for failed, etc.). Something like that would be nice to have for Backrest as well. Basically if I spotted a red cross in my system tray, I would start to investigate.

Additional context This is what they look like for Duplicati: