Remove RTOS targets from the supported embedded platforms section (non-LTS releases)

Remove the INTEGRITY, QNX, and VxWorks targets from the supported embedded platforms section (https://doc.qt.io/qt-6/supported-platforms.html#embedded-platforms) for all non-LTS releases (Qt 6.9, Qt 6.10, Qt 6.11). 

Add the following note at the beginning of the supported embedded platforms section:

Note  The INTEGRITY, QNX, and VxWorks targets are only supported in Long Term Support (LTS) releases. To get support for those targets in non-LTS releases, contact Qt Professional Services (https://www.qt.io/qt-professional-services).