Create new phase for bug trimming

[NorbertLoh]

Is your feature request related to a problem? Please describe.
This new feature is a sub-feature for #1301.

Describe the solution you'd like
The solution should aim to create a new phase and a page where the new features should go

Describe alternatives you've considered
Previously students would manually delete bugs in the bug reporting phase. However, there is no way to reopen deleted issues.

Additional context
Add any other context or screenshots about the feature request here.

[damithc]

This new feature is a sub-feature for #1301.

I've added it as a sub-issue of #1301, using GitHub's new sub-issues feature.