Add zuul:value xref

Use it and zuul:attr xrefs.

Change-Id: I5cac10bbf76b54d0f035cc7c69e9304a2e197303
diff --git a/doc/source/user/gating.rst b/doc/source/user/gating.rst
index 3398892..c1d04a7 100644
--- a/doc/source/user/gating.rst
+++ b/doc/source/user/gating.rst
@@ -41,7 +41,7 @@
 developers to create changes at a rate faster than they can be tested
 and merged.
 
-Zuul's :ref:`dependent pipeline manager<dependent_pipeline_manager>`
+Zuul's :value:`dependent pipeline manager<pipeline.manager.dependent>`
 allows for parallel execution of test jobs for gating while ensuring
 changes are tested correctly, exactly as if they had been tested one
 at a time.  It does this by performing speculative execution of test