Fix issues in v6.1.0 with SWUpdate and libubootenv

Fixes: https://git.kontron-electronics.de/sw/ked/plan/plan-yocto/-/issues/1268 and https://git.kontron-electronics.de/sw/ked/plan/plan-yocto/-/issues/1274

• Add support for libubootenv YAML config in SWUpdate (backport)
• Upgrade libubootenv to v0.3.5 to support common implementation of libuboot_namespace_from_dt()
• Set provider for u-boot-fw-utils to libubootenv-bin on distro level
• Install u-boot-fw-utils by default in image-ked* images
• Update changelog in docs