[TASK] Add a code of conduct document

Having a CODE_OF_CONDUCT.md document that links to the TYPO3 code
of conduct provides users who view the project source on GitHub
easy, direct access to the full text.

Releases: main, 11.5, 10.4
Resolves: #97376
Change-Id: I6509b402a5229cbd926ce42b4fd6a1c0e60e0fc2
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74291


Tested-by: core-ci <typo3@b13.com>
Tested-by: Mathias Bolt Lesniak <mathias@pixelant.no>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Lina Wolf <112@linawolf.de>
Reviewed-by: Mathias Bolt Lesniak <mathias@pixelant.no>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Lina Wolf <112@linawolf.de>

CODE_OF_CONDUCT.md

+# Code of Conduct
+
+This project uses the
+[TYPO3 Code of Conduct](https://typo3.org/community/values/code-of-conduct).
+
+When you contribute to this project or interact with community members,
+you agree to adhere to this code of conduct.