Add generic down page

[jorg-vr]

This pr adds a status page, indicating that dodona is down unexpectedly, with historic incidents.

It also adds an under maintenance page, for scheduled outages

• adjust scheduled outage times to actual plan

[bmesuere]

Can you add a date and time?

[jorg-vr]

As we are currently up I wouldn't add current date and time?
But I might leave this pr open for a future usecase

[bmesuere]

The idea is to have a page where we can link to from status.dodona.be (instead of the current page). It should show an overview of current and past issues. For all past issues, the goal should be to display the time period during which the issue took place and the reason.

[jorg-vr]

@bmesuere does this update align with your expectations?

[jorg-vr]

@bmesuere I've added a planned outages page here as well to the incidents page for unplanned outages.

[bmesuere]

I have set up a Saas solution at better stack instead. In case of issues and maintenance, we want it to be as easy as possible to update the status.

The statuspage can be found at https://status.dodona.be/

It contains

• an automatic monitor that checks if dodona.be is available
• a history of the uptime
• slack notifications in case of problems
• the ability to create an "incident" and add status updates to that
• the ability to plan a maintenance window and add status updates to that