Feature request: update the paused migrators status page

[ruben-arts]

I would love to see the status of the arm_variant_tegra migration. But this currently doesn't seem updated as there are currently tegra builds for the nccl package available after this PR: conda-forge/nccl-feedstock#151

This FR is created as a tip by @h-vetinari in zulip#general > Jetson Nano support pytorch

[h-vetinari]

FWIW, I think this would be beneficial in other cases too. We're regularly using paused migrators to ramp up something before actually starting the migration.

The bigger issue is that the bot currently is only able to mark anything done if it opened a PR itself and it got either merged or closed. IMO we could improve detection there though, to the point that if the (migrator name, timestamp, migration_number) tuple already exists on the feedstock, the bot can assume it has been done (this would, by the way, also be very helpful with avoiding pointless PRs for already-done migrations when pushing new branches: #2500)