fix(docs): add readthedocs configuration file

Readthedocs uses weird defaults and the web interface gives limited
configuration options. Add the config file to allow them to be changed.

Bump build os image to Ubuntu 22.04 to be in line with the CI.

Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Change-Id: I1a620b15ab3924244f305056096024fe117c63dd
(cherry picked from commit 8a84776340bf4215d235b7b6dc09cf94aed8c6b3)
Signed-off-by: Yann Gautier <yann.gautier@st.com>
1 file changed