Article: guide configuring maintenance windows

[spokanemac]

Article: Guide configuring maintenance windows in Fleet. https://github.com/fleetdm/fleet/issues/20763

cc: @getvictor @sharon-fdm

[spokanemac]

Since this feature has already shipped, we could publish ASAP.

[sharon-fdm]

@spokanemac, awesome writing! See comments.

[lukeheath]

@spokanemac I almost merged this, but then remembered that we likely want to hold this and any articles or guides about scheduled maintenance until we have the DDM OS update flow in place.

[lukeheath]

Converting to draft since we want to wait to publish this until we have more time to work on the feature.