Bugfixes

• #5405: Fixes issue where model always gets retrained if multiple NLU/story files are in a
  directory, by sorting the list of files.
• #5444: Fixed ambiguous logging in DIETClassifier by adding the name of the calling class to the log message.

[\#5506](https://github.com/rasahq/rasa/issues/5506): Set default value for `weight_sparsity` in `ResponseSelector` to `0`.

:   This fixes a bug in the default behaviour of `ResponseSelector` which was accidentally introduced in `rasa==1.8.0`.
    Users should update to this version or `rasa>=1.9.3` and re-train their models if `ResponseSelector` was used in their pipeline.

Improved Documentation

• #5302: Improved documentation on how to build and deploy an action server image for use on other servers such as Rasa X deployments.