services: add maintenance mode option to snooze alert notifications

[Forfold]

Closes #2490

Adds a button to configure maintenance mode for 1, 2, or 4 hours from any service details page. All notifications during this time period will be silenced, and escalations will not be processed. Any incoming alerts will still be created (snoozing integration keys out of scope).

After maintenance mode ends, alerts will be sent out as normal to the on-call user.

Screenshots:

Service details maintenance mode button

Maintenance mode dialog

Maintenance mode notice banners

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Escalate alert GraphQL error while in maintenance mode

[mastercactapus]

For the escalation code, I had a couple of thoughts, what's the expected behavior when escalating multiple alerts when only one or two are in maintenance mode?

When we talked about it, we figured an error should be returned, but the method signatures suggest we should instead have it do nothing, as it's supposed to return only the alerts that were escalated.

escalateAlerts(input: [1]) -> []

As it stands, if one alert is for a service in maintenance mode, all will fail with a generic error. It's more a limitation of how the API is set up currently.

I'll reach out to chat more about it

[Forfold]

@mastercactapus

For the escalation code, I had a couple of thoughts, what's the expected behavior when escalating multiple alerts when only one or two are in maintenance mode?

totally did not think of this use case, we were thinking in terms of escalateAlerts(input: [id]) the whole time since we were only testing with one alert. I think it makes sense to return maybe an array of true/error or something similar?

alert 1: active service
alert 2: maint. mode service

escalateAlerts(ids: [1, 2])

returns

{
  "errors": [{
    message: "escalate alert 2: in maintenance mode",
    path: ['escalateAlerts']
  }],
  "data": {
    "1": true
  }
}