Explicitly filter out Sanic warnings after Sanic is initialized

[aleksandarmijat]

Proposed changes:

• Explicitly filter out Sanic warnings after Sanic is initialized

Status (please check what you already did):

• [ ] made PR ready for code review
• [ ] added some tests for the functionality
• [ ] updated the documentation in the rasaHQ/rasa
• [ ] updated the changelog (please check changelog for instructions)
• [ ] reformat files using black (please check Readme for instructions)

[Tawakalt]

Do we need a changelog?

[radovanZRasa]

We should at list have a misc changelog.