readthedocs: add configuration file

readthedocs needs a configuration file with the
name .readthedocs.yaml.

See:
https://docs.readthedocs.io/en/stable/config-file/

Change-Id: I594cdb2650322222661b2069128fb4190052f37d
Signed-off-by: Adrian Vladu <avladu@cloudbasesolutions.com>

.readthedocs.yaml

@@ -0,0 +1,17 @@
+version: 2
+
+build:
+  os: "ubuntu-22.04"
+  tools:
+    python: "3.11"
+
+formats: all
+
+sphinx:
+  configuration: doc/source/conf.py
+
+python:
+  install:
+    - path: .
+    - requirements: doc/requirements.txt
+