[DOCS] Add important RST for changed form framework markup

Resolves: #103392
Related: #103117
Releases: main, 12.4
Change-Id: I97f9c68b6ad1c6b3ded4c70a82dbfe20eb5a9f20
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83456


Tested-by: Chris Müller <typo3@krue.ml>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Chris Müller <typo3@krue.ml>
Tested-by: core-ci <typo3@b13.com>

typo3/sysext/core/Documentation/Changelog/12.4.x/Important-103117-FormFrameworkSelectMarkupChanged.rst

+.. include:: /Includes.rst.txt
+
+.. _important-103392-1710345611:
+
+=========================================================
+Important: #103392 - Form framework select markup changed
+=========================================================
+
+See :issue:`103392`
+
+Description
+===========
+
+With :issue:`103117`, the `elementClassAttribute` of the "SingleSelect",
+"CountrySelect" and "MultiSelect" fields got changed from `form-control` to
+`form-select` in EXT:form, as defined by `Bootstrap`_, if the Bootstrap 5 markup
+(:yaml:`templateVariant: version2`) is used.
+
+If needed, the old markup can be restored by overriding the configuration as
+follows:
+
+..  code-block:: yaml
+    :emphasize-lines: 9,15,21
+
+    prototypes:
+      standard:
+        formElementsDefinition:
+          CountrySelect:
+            variants:
+              -
+                identifier: template-variant
+                properties:
+                  elementClassAttribute: form-control
+          MultiSelect:
+            variants:
+              -
+                identifier: template-variant
+                properties:
+                  elementClassAttribute: form-control
+          SingleSelect:
+            variants:
+              -
+                identifier: template-variant
+                properties:
+                  elementClassAttribute: form-control
+
+.. _Bootstrap: https://getbootstrap.com/docs/5.3/forms/select/
+
+.. index:: Frontend, ext:form