Add port monitors to maintenance windows

[ajh123]

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Currentlly Checkmate only allows HTTP(S) monitors to be included in maintenance windows. However some services (like databases) only expose a none HTTP port. This means if you want to announce maintenance for these services you cannot.

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Make port monitors appear in the drop down menu in the maintenance settings.

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Add other types of monitors in the drop down too - however the port monitor is the most generic and would be widely used.

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[jasneetsingh6114]

Hey can I work on this issue?

[ajh123]

Hey can I work on this issue?

@jasneetsingh6114 I'm not part of the Checkmate team, but I suppose you can.

[ajhollid]

@jasneetsingh6114 sure it's all yours