[docs] Add .readthedocs.yaml config.

This fixes an issue that prevents the documentation from being built.
See https://blog.readthedocs.com/migrate-configuration-v2/

Signed-off-by: Michael Seifert <m.seifert@digitalernachschub.de>

Author: seifertm

.readthedocs.yaml

@@ -0,0 +1,18 @@
+---
+# Read the Docs configuration file for Sphinx projects
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+version: 2
+build:
+  os: ubuntu-22.04
+  tools:
+    python: '3.12'
+
+sphinx:
+  configuration: docs/source/conf.py
+  fail_on_warning: true
+
+python:
+  install:
+  - requirements: dependencies/default/constraints.txt
+  - requirements: dependencies/docs/constraints.txt