Document "Controlled Self-Recursion Support" for 7.6

Preview page: https://preview.docs-test.couchbase.com/recursion_param2/server/current/eventing/eventing-advanced-keyspace-accessors.html#optional-params-recursion

PR: https://github.com/couchbaselabs/docs-devex/pull/141

Document new content for Eventing for the 7.6 Server release.

Controlled self-recursion support: if the optional "self_recursion" flag is set to true, Eventing doesn't suppress the recursive source bucket mutation and instantly processes the mutation that was just created

Slide: https://docs.google.com/presentation/d/11FpUOa2iH1yVErPHEbVe2IcU3gs5RTNGqcAP4SrTAUw/edit#slide=id.g292548574fe_1_0