check if ActionExecutionRejected should be thrown after custom action for slot validations was called

[wochinge]

Proposed changes:

• fix Send potential ActionExecutionRejected after form validation #6977
• check for a required ActionExecutionRejection error after custom action for slot validations / extractions was called. This doesn't reject forms before users could intervene.
• don't deactivate the form in case the user manually returned a ActionExecutionRejected event
• raise InvalidDomain instead of ValueError for invalid slot mappings to avoid unnecessary Sentry errors
• a custom action can reject its execution by returning a ActionExecutionRejected event and still apply other events (e.g. slots)
• update related documentation

Status (please check what you already did):

• added some tests for the functionality
• updated the documentation
• updated the changelog (please check changelog for instructions)
• reformat files using black (please check Readme for instructions)

[Ghostvv]

please update the docs as part of this PR, otherwise looks good to me 🚀

[wochinge]

@ArjaanBuijk Could you please check the documentation?

[wochinge]

@tczekajlo The security check for the secrets is currently failing. it's not required but I think we need to exclude mdx files from the check

[wochinge]

@melindaloubser1 Requested review from you since @ArjaanBuijk doesn't seems to be busy

[indam23]

I made some small phrasing changes directly since it won't allow me to request changes on deleted lines

[wochinge]

Thank you so much for this blazing fast review and changes @melindaloubser1 🙌

[wochinge]

@Ghostvv I'm gonna dismiss your changes requested because you said it's good to go apart from the docs and they were approved now.

docs are there and requested changes were worked in