doc: Set dependent layers and external links to reference main/master versions

This patch changes the external links to reference:

  * Linux Yocto 5.15
  * Yocto Project latest documentation

And sets the appropriate dependent layer revisions for the EWAOL main branch.

Issue-Id: SCM-4394
Signed-off-by: Richard Neill <richard.neill@arm.com>
Change-Id: I534391bf3de7b41fbf3d2ff9f781f6409ef045f9