Backport PR #39669: DOC: Start v1.2.3 release notes (#39694)

Co-authored-by: Simon Hawkins <[email protected]>

Author: meeseeksmachine

doc/source/whatsnew/index.rst

@@ -16,6 +16,7 @@ Version 1.2
 .. toctree::
    :maxdepth: 2
 
+   v1.2.3
    v1.2.2
    v1.2.1
    v1.2.0

doc/source/whatsnew/v1.2.2.rst

@@ -46,4 +46,4 @@ Bug fixes
 Contributors
 ~~~~~~~~~~~~
 
-.. contributors:: v1.2.1..v1.2.2|HEAD
+.. contributors:: v1.2.1..v1.2.2

doc/source/whatsnew/v1.2.3.rst

@@ -0,0 +1,48 @@
+.. _whatsnew_123:
+
+What's new in 1.2.3 (March ??, 2021)
+------------------------------------
+
+These are the changes in pandas 1.2.3. See :ref:`release` for a full changelog
+including other versions of pandas.
+
+{{ header }}
+
+.. ---------------------------------------------------------------------------
+
+.. _whatsnew_123.regressions:
+
+Fixed regressions
+~~~~~~~~~~~~~~~~~
+
+-
+-
+
+.. ---------------------------------------------------------------------------
+
+.. _whatsnew_123.bug_fixes:
+
+Bug fixes
+~~~~~~~~~
+
+-
+-
+
+.. ---------------------------------------------------------------------------
+
+.. _whatsnew_123.other:
+
+Other
+~~~~~
+
+-
+-
+
+.. ---------------------------------------------------------------------------
+
+.. _whatsnew_123.contributors:
+
+Contributors
+~~~~~~~~~~~~
+
+.. contributors:: v1.2.2..v1.2.3|HEAD