Improve debugging of what files are causing slow Mutagen sync

[rfay]

Expected Behavior

ddev start should take something like 30-60s on most environments.

Actual Behavior

In some environments, it can take a huge amount of time, up to 30m. Someone at Drupalcon Portland 2024 explained this to me on the Intel Mac. We weren't easily about to debug it at the time.

Steps To Reproduce

Create a large file and put it in the root of a repository. ddev mutagen reset && ddev restart. It can take some serious time.

One can see this process going on with

while true; do ddev mutagen st -l | grep "^Current"; sleep 1; done

but that is not really suggested in the docs and it would be an improvement.

We could also make ddev mutagen st take a --continuous argument and that would really help people.

Anything else?

We used to show the mutagen sync process as it went along, displaying what file was being synced. That made it much easier to debug. But we replaced that with dots at some point.