Return 449 status code if the Domain is not stored or missing in the …

[aleksandarmijat]

Proposed changes:

• Checks the domain in the payload and return 449 status code if the domain is missing (both stored and in the payload) or stale (digest mismatch).

Status (please check what you already did):

• [x] 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)
• [x] reformat files using black (please check Readme for instructions)

[CLAassistant]

All committers have signed the CLA.

[aleksandarmijat]

Spike got approved, closing this PR, will be used as the inspiration for the implementation.