Improve Rasa CLI start-up time

[federicotdn]

Rasa version: master

Python version: 3.5, 3.6, 3.7

Operating system (windows, osx, ...): GNU/Linux, macOS, Windows

Issue:

After a fresh rasa install, the rasa CLI can take up to 1.5 seconds (on my system) to show any output, even when no action has been specified (e.g. rasa --help). For workflows that involve running the rasa command various times, this can be an inconvenience. We should aim to lower the start-up time for the CLI to under 1 second, or another set number that users will be comfortable with.

Related to: #4248 and #3010.

Tools that could be useful:

• https://docs.python.org/3.7/library/profile.html
• https://github.com/jrfonseca/gprof2dot
• https://github.com/joerick/pyinstrument

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[koaning]

During a recording I just noticed 10+ seconds. Now, we need to be careful here because the recording is most likely influencing the timing but it seems like Rasa currently can take an order of magnitude more than the 1.5 seconds mentioned in the issue.