DOC-12631 temporary fix replication.adoc code samples

Fixing the code samples will require collaboration with @borrrden and co,
but in the meantime, we can copy the previous snippets from version 3.0.

This requires copying the "simplified" version from #910
and making some changes:

* fix image location to :ROOT:
* remove additional == 2 levels of header

as well as copy/pasting code from the previous output into the source snippets as appropriate.