[ATO-2105] Implement functionality to create custom spans

[Tawakalt]

Proposed changes:

• Fixes ATO-2105

Views from Jaegar UI

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)

[ancalita]

Great work 💯 In addition to the below comments, how did you obtain that view in Jaeger? I'd suggest to add a new test custom action that does the same steps you took to get that custom span in a different test case.

[Tawakalt]

Great work 💯 In addition to the below comments, how did you obtain that view in Jaeger? I'd suggest to add a new test custom action that does the same steps you took to get that custom span in a different test case.

It will require an integration test to achieve this.

I wrote a custom action like this and triggered it

class ValidatePredefinedSlots(ValidationAction):
    def validate_location(
        self,
        slot_value: Any,
        dispatcher: CollectingDispatcher,
        tracker: Tracker,
        domain: DomainDict,
    ) -> Dict[Text, Any]:
        """Validate location value."""
        from rasa_sdk.tracing.tracer_register import ActionExecutorTracerRegister

        tracer = ActionExecutorTracerRegister().get_tracer()
        with tracer.start_as_current_span("my_very_own_custom_span"):
            if isinstance(slot_value, str):
                # validation succeeded, capitalize the value of the "location" slot
                dispatcher.utter_message("Nice! I've always wanted to visit ", slot_value.capitalize())
                return {"location": slot_value.capitalize()}
            else:
                # validation failed, set this slot to None
                return {"location": None}

[ancalita]

🎉
I'd also make Sanchari aware of this integration test case need to be added to the list for the action server testing.