Add `:in_progress` status to errors

[kelvinst]

Is your feature request related to a problem? Please describe. I like to mark errors as triaged as soon as I create a ticket on the project management tool to deal with it, so that I can know if there are new, untriaged errors, just by looking at the error list.

Describe the solution you'd like I like that in other error trackers, AppSignal for example, you can mark an error as "Work In Progress", to signalize there's someone working on the fix for it. Maybe, besides the new status, it would be good to have a "Notes", or "Comments" feature in the error/occurrence page, but that might deserve it's own separate PR, IDK.

PS.: an error that is marked as "In Progress" should not reset to "Unresolved" if a new occurrence comes up, just the "Resolved" ones.

Describe alternatives you've considered Maybe mark them as resolved? But still, if the error reoccurs, it is marked as unresolved again, so we lose track of that.

Additional context How it works on AppSignal:

[kelvinst]

I can totally work on it if you say you want to do it.

[Terbium-135]

I like that proposal. Sometimes it is too easy to mark an error as resolved