[TASK] Add missing Documentation/9.0/Index.rst

Due to the missing index file, the 9.0 doc files
are not yet rendered on docs.typo3.org

Change-Id: I65781b9de84dd4a0f1205ded175858a90dc01f85
Resolves: #83304
Releases: master
Reviewed-on: https://review.typo3.org/55056


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>

typo3/sysext/core/Documentation/Changelog/9.0/Index.rst

+
+.. include:: ../../Includes.txt
+
+9.0 Changes
+===========
+
+**Table of contents**
+
+.. contents::
+   :local:
+   :depth: 1
+
+Breaking Changes
+^^^^^^^^^^^^^^^^
+
+.. toctree::
+   :maxdepth: 1
+   :titlesonly:
+   :glob:
+
+   Breaking-*
+
+Features
+^^^^^^^^
+
+.. toctree::
+   :maxdepth: 1
+   :titlesonly:
+   :glob:
+
+   Feature-*
+
+Deprecation
+^^^^^^^^^^^
+
+.. toctree::
+   :maxdepth: 1
+   :titlesonly:
+   :glob:
+
+   Deprecation-*
+
+Important
+^^^^^^^^^
+
+.. toctree::
+   :maxdepth: 1
+   :titlesonly:
+   :glob:
+
+   Important-*