migration-guides: start of 4.3 migration and release notes

From notes from Richard Purdie

(From yocto-docs rev: 62fcaabd06558669034e8732b8d22a9c46e36cf2)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
CC: richard.purdie@linuxfoundation.org
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/migration-guides/release-notes-4.3.rst

@@ -0,0 +1,55 @@
+.. SPDX-License-Identifier: CC-BY-SA-2.0-UK
+
+Release notes for 4.3 (nandbield)
+----------------------------------
+
+New Features / Enhancements in 4.3
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+-  Linux kernel 6.x, glibc 2.xx and ~xxx other recipe upgrades
+
+-  New variables:
+
+-  Architecture-specific enhancements:
+
+-  Kernel-related enhancements:
+
+-  New core recipes:
+
+-  QEMU/runqemu enhancements:
+
+-  Image-related enhancements:
+
+-  wic Image Creator enhancements:
+
+-  SDK-related improvements:
+
+-  Testing:
+
+-  Utility script changes:
+
+-  BitBake improvements:
+
+   -  The BitBake Cooker log now contains notes when the caches are
+      invalidated which is useful for memory resident bitbake debugging.
+
+-  Packaging changes:
+
+-  Miscellaneous changes:
+
+Known Issues in 4.3
+~~~~~~~~~~~~~~~~~~~
+
+Recipe License changes in 4.3
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following corrections have been made to the :term:`LICENSE` values set by recipes:
+
+Security Fixes in 4.3
+~~~~~~~~~~~~~~~~~~~~~
+
+Recipe Upgrades in 4.3
+~~~~~~~~~~~~~~~~~~~~~~
+
+Contributors to 4.3
+~~~~~~~~~~~~~~~~~~~