Allow choice of reloader type

[oelhammouchi]

I know it was closed in #5007, but would it be possible to reconsider this? I'm having a lot of trouble with watchdog despite following all the fixes proposed such as #2603. The reloader constantly detects spurious file changes, whereas I've never experienced such issues with stat. If you really dislike the idea of a new flag, maybe an environment variable would be an option?

Thanks a lot for the work on this awesome package!

[davidism]

My comment in #5007 (comment) still applies. The solution is to fix the reloader, not to provide a toggle that users shouldn't need. If you have an issue with the reloader, create a minimal reproducible example and report that to Werkzeug or Watchdog.