Set version 6.3 and release date in changelog

Merged-by: Martin Grzenia <martin.grzenia@iml.fraunhofer.de>

Author: martingr

opentcs-documentation/src/docs/release-notes/changelog.adoc

@@ -16,7 +16,7 @@ The openTCS developers
 This change log lists the most relevant changes for past releases in reverse chronological order.
 (Note that the openTCS project adheres to https://semver.org/[Semantic Versioning].)
 
-== Unreleased
+== Version 6.3 (2025-02-04)
 
 * New features and enhancements:
 ** Add support for transport order type priorities.