Non-stack based PR/MR view

PR/MR view is very useful, but one big limitation of it is that it’s linked to one specific stack.

It would be very useful to have a PR/MR view that shows all MRs known to Spacelift. When an MR is selected, it would show you all stacks involved with it (and an easy way to reach all proposed runs and their status).

The view would also allow you to filter on space, tags, etc …

This would be very useful for situations where MRs/PRs touch multiple Spacelift stacks.