doc: cleanup references to conductor doc

The conductor doc is not really end user material,
so this moves it under reference/, removes it from the
user page and adds it to the reference index for internals.
Also makes the contributor page link to the reference internals
since it's kind of weird to have one contributor section that
only mentions one thing but the internals under reference have
a lot more of that kind of detail. Finally, a todo is added so
we don't forget to update the reference internals about versioned
objects at some point since that's always a point of confusion
for people.

Change-Id: I8d3dbce5334afaa3e1ca309b2669eff9933a0104

doc/source/contributor/index.rst

@@ -104,8 +104,6 @@ changes done to the API, as the impact can be very wide.
 Nova Major Subsystems
 =====================
 
-Major subsystems in nova have different needs; some of those are documented
-here. If you are contributing to one of these please read the subsystem guide
-before diving in.
-
-* :doc:`/user/conductor`
+Major subsystems in nova have different needs. If you are contributing to one
+of these please read the :ref:`reference guide <reference-internals>` before
+diving in.

doc/source/index.rst

@@ -223,6 +223,7 @@ looking parts of our architecture. These are collected below.
    contributor/project-scope
    contributor/ptl-guide
    reference/api-microversion-history.rst
+   reference/conductor
    reference/gmr
    reference/i18n
    reference/live-migration
@@ -245,7 +246,6 @@ looking parts of our architecture. These are collected below.
    user/cells
    user/cellsv2-layout
    user/certificate-validation
-   user/conductor
    user/feature-classification
    user/filter-scheduler
    user/flavors

doc/source/reference/index.rst

@@ -6,6 +6,8 @@ The nova project is large, and there are lots of complicated parts in it where
 it helps to have an overview to understand how the internals of a particular
 part work.
 
+.. _reference-internals:
+
 Internals
 =========
 
@@ -28,6 +30,10 @@ The following is a dive into some of the internals in nova.
   ``ComputeDriver.update_provider_tree`` method.
 * :doc:`/reference/upgrade-checks`: A guide to writing automated upgrade
   checks.
+* :doc:`/reference/conductor`
+
+.. todo:: Need something about versioned objects and how they fit in with
+          conductor as an object backporter during upgrades.
 
 Debugging
 =========

doc/source/user/index.rst

@@ -27,7 +27,8 @@ Architecture Overview
   to connect specific block devices to computes. This deserves its own deep
   dive.
 
-* :doc:`Conductor </user/conductor>`: TODO
+See the :ref:`reference guide <reference-internals>` for details about more
+internal subsystems.
 
 Deployment Considerations
 -------------------------