Build: allow users to use Ubuntu 22.04 LTS (#9009)

Ubuntu 22.04 LTS is not yet released, but it's already available to use. We can
start allowing people to use this image for their builds.

Author: humitos

readthedocs/settings/base.py

@@ -537,6 +537,7 @@ def TEMPLATES(self):
         # Mapping of build.os options to docker image.
         'os': {
             'ubuntu-20.04': f'{DOCKER_DEFAULT_IMAGE}:ubuntu-20.04',
+            'ubuntu-22.04': f'{DOCKER_DEFAULT_IMAGE}:ubuntu-22.04',
         },
         # Mapping of build.tools options to specific versions.
         'tools': {

scripts/compile_version_upload_s3.sh

@@ -89,7 +89,7 @@ set -x # Echo commands
 
 # Define variables
 SLEEP=350 # Container timeout
-OS="ubuntu-20.04" # Docker image name
+OS="${OS:-ubuntu-22.04}" # Docker image name
 TOOL=$1
 VERSION=$2