Ambiguous neutron-ovn setup docs

Following up on this thread [1], the neutron-ovn setup is confusing. Looking in the "networking-ovn/latest" doc some of the necessary steps are to configure the core_plugin and service_plugin like this:

core_plugin = neutron.plugins.ml2.plugin.Ml2Plugin
service_plugins = networking_ovn.l3.l3_ovn.OVNL3RouterPlugin

This seems to fail when starting neutron-server. In the manual neutron installation guide to set up neutron-ovn [2] the config is slightly different:

core_plugin = ml2
service_plugins = ovn-router

According to the OP the latter config options seem to work. This should be merged to have unambiguous documentation steps across the different pages.

[1] https://stackoverflow.com/questions/76080216/error-neutron-modulenotfounderror-no-module-named-networking-ovn?noredirect=1#comment134210960_76080216
[2] https://docs.openstack.org/neutron/latest/install/ovn/manual_install.html

This bug tracker is for errors with the documentation, use the following as a template and remove or add fields as you see fit. Convert [ ] into [x] to check boxes:

- [X] This doc is inaccurate in this way: There different doc versions for the same setup, one of them doesn't work.
- [ ] This is a doc addition request.
- [ ] I have a fix to the document that I can paste below including example: input and output.

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-----------------------------------
Release: on 2019-01-23 11:29:27
SHA: eda5d7f80d877601170631c5f5485370ea701f42
Source: https://opendev.org/openstack/networking-ovn/src/doc/source/install/manual.rst
URL: https://docs.openstack.org/networking-ovn/latest/install/manual.html