Remove ~missed-SLO when the severity label is downgraded or removed
Problem to solve
Note: SLO is attached to severity label since #400 (closed).
If an issue has a ~"missed-SLO" label, and the severity label is downgraded, then the ~"missed-SLO" label might no longer be correct. An example is https://gitlab.com/gitlab-org/gitlab-ee/issues/10661#note_188276506 where ~S2 was re-evaluated to ~S3.
Or, if the severity label is removed entirely, then the ~"missed-SLO" label no longer applies.
Proposal
There should be a policy that reviews all open issues with a ~"missed-SLO" label, and removes the label if the SLO has not been reached or the severity label has been removed.
Further details
This would help with re-grooming in the case where someone modifies a severity label but forgets to remove the ~"missed-SLO" label.
@godfat @markglenfletcher @rymai @tpazitny @at.ramya a suggestion as I went through the backlog of bugs.