Bugfix/pass metadata to remote action start event

[kaustuk]

Proposed changes:

• Fixed issue: custom action_session_start can't access user message metadata #7420
• Have created the PR as per the first approach mentioned here custom action_session_start can't access user message metadata #7420 (comment). This is just the producer part. Need to create PR for consumer part as well. But still don't know if that is good enough. This change will not break anything existing code as such.

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)

[CLAassistant]

All committers have signed the CLA.

[sara-tagger]

Thanks for submitting a pull request 🚀 @Imod7 will take a look at it as soon as possible ✨

[wochinge]

closing this PR as it will be fixed by #7922