RTD is deprecating some config options, so RTD build will fail

Find all files called .readthedocs.yaml   (in root directory of all our repos, all branches)

Ref:
https://wiki.o-ran-sc.org/pages/diffpagesbyversion.action?pageId=12157500&selectedPageVersions=21&selectedPageVersions=19

Ref:
https://docs.readthedocs.io/en/latest/config-file/v2.html#build-os

Note. This file is not used in the Jenkins RTD verify job, so the only way to actually check if this worked is to check the build for each project on "readthedocs.org" after merge:
e.g. https://readthedocs.org/projects/o-ran-sc-nonrtric-plt-ranpm/builds/
e.g. https://readthedocs.org/projects/o-ran-sc-nonrtric/builds/