[DOCS] Document new default value for UTF-8 filesystems

With #98090 TYPO3_CONF_VARS['SYS']['UTF8filesystem'] was set to true for new installations. This should also be documented in the changelog.

Resolves: #98144
Related: #98090
Releases: main
Change-Id: Ia18c0347c745967586a47ff5167327bac283051e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75445


Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>

typo3/sysext/core/Documentation/Changelog/12.0/Important-98090-UsePreconfiguredUTF8FilesystemOnFirstInstallation.rst

+.. include:: /Includes.rst.txt
+
+.. _important-98090-1660490213:
+
+============================================================================
+Important: #98090 - Use preconfigured UTF-8 filesystem on first installation
+============================================================================
+
+See :issue:`98090`
+
+Description
+===========
+
+Back in the old and dark days, some filesystems did not know about "special"
+chars. TYPO3 has the :php:`TYPO3_CONF_VARS` toggle :php:`['SYS']['UTF8filesystem']`
+to declare if filesystems are UTF-8 aware.
+
+This toggle is :php:`false` by default since ever. It triggers functionality to
+rename any file that contains characters like umlauts, or maybe entirely consist
+of "special" chars only (japanese) to something "safe".
+
+This is a usability issue since information is lost and language-specific
+characters are destroyed.
+
+Nowadays every serious filesystem supports UTF-8.
+
+There are no issues related to UTF8filesystem=true for years.
+
+The patch now sets UTF8filesystem=true for new installations to see if anything
+still pops up. If that works out, we'll continue with further patches in v13 to
+further phase out the option entirely.
+
+.. index:: LocalConfiguration, ext:core