Add 2023.1 specs directory

Using release number here. In Zed cycle, TC passed a resolution[1] and
updated the release Identification document[2] to use the release
number as primary identifier in the development cycle. Release name
will be used in marketting and release team tooling (until they are
migrated to work with release number) only.

[1] https://governance.openstack.org/tc/resolutions/20220524-release-identification-process.html
[2] https://governance.openstack.org/tc/reference/release-naming.html

Signed-off-by: Yasufumi Ogawa <yasufum.o@gmail.com>
Change-Id: I9c56ef2a1bbce716a37cac83e4316e37d989b386

doc/source/index.rst

@@ -22,6 +22,7 @@ Specifications
    :glob:
    :maxdepth: 2
 
+   specs/2023.1/index
    specs/zed/index
    specs/yoga/index
    specs/xena/index

specs/2023.1/index.rst

@@ -0,0 +1,9 @@
+============================
+Tacker 2023.1 Specifications
+============================
+
+.. toctree::
+   :glob:
+   :maxdepth: 1
+
+   *

specs/2023.1/placeholder.rst

@@ -0,0 +1,124 @@
+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+==================
+(Placeholder Spec)
+==================
+
+This file is just a placeholder for the specs directory.
+It will be removed soon after some spec is merged.
+
+The latest spec template is found at ``specs/template.rst``
+in the ``tacker-specs`` repository.
+
+Problem description
+===================
+
+Sphinx toctree complains if no file exists in a directory
+specified in toctree glob.
+
+Use Cases
+---------
+
+None
+
+Proposed change
+===============
+
+Add this file. Please remove later when the another spec is approved.
+
+Alternatives
+------------
+
+None
+
+Data model impact
+-----------------
+
+None
+
+REST API impact
+---------------
+
+None
+
+Security impact
+---------------
+
+None
+
+Notifications impact
+--------------------
+
+None
+
+Other end user impact
+---------------------
+
+None
+
+Performance Impact
+------------------
+
+None
+
+Other deployer impact
+---------------------
+
+None
+
+Developer impact
+----------------
+
+None
+
+Upgrade impact
+--------------
+
+None
+
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+None
+
+Work Items
+----------
+
+None
+
+
+Dependencies
+============
+
+None
+
+
+Testing
+=======
+
+None
+
+
+Documentation Impact
+====================
+
+None
+
+References
+==========
+
+None
+
+
+History
+=======
+
+None

specs/yoga/placeholder.rst

@@ -1,3 +0,0 @@
-====================
-Placeholder for Yoga
-====================

specs/zed/placeholder.rst

@@ -1,3 +0,0 @@
-===================
-Placeholder for Zed
-===================