Doc clarification: Mule message propagation in source policies

[AdamCoulterOz]

This seems incorrect:

docs-gateway/mule-gateway/modules/ROOT/pages/policies-custom-mule-4-reference.adoc

Lines 424 to 425 in 1156e35

	For source policies, any modification to a Mule Message made after the `http-policy:execute-next` element, will
	continue propagation throughout the rest of the Mule event processing chain.

It should say:

For source policies, any modification to a Mule Message made after the http-policy:execute-next element, will implicitly continue propagation through the rest of the return path in the Mule event processing chain.

This removes a possible ambiguity in the wording which could be understood as "modifications made after the http-policy:execute-next" are what get propagated into the processing chain (i.e. by the api implementation).

[chris-campbell9]

@AdamCoulterOz Thank you for your contribution. We have added it to our issue tracking system for review.