[ubicloud] Persist GitHub context to a file

GitHub environment variables are only available in the workflow, not for
unix user. We need some of these variables to run some features such as
Ubicloud Cache. Runner script allows to run a hook script before the job
starts and this hook has access to the environment variables. So we just
persist them to a file and read them in the Ubicloud Cache proxy.

images/ubuntu/scripts/ubicloud/setup-runner-user.sh

@@ -49,6 +49,20 @@ exec env -- "\${env[@]}" ./actions-runner/run.sh --jitconfig "\$1"
 EOT
 chmod +x ./actions-runner/run-withenv.sh
 
+# GitHub environment variables are only available in the workflow, not for unix
+# user. We need some of these variables to run some features such as Ubicloud
+# Cache. Runner script allows to run a hook script before the job starts and
+# this hook has access to the environment variables. So we just persist them
+# to a file and read them in the Ubicloud Cache proxy.
+# See https://docs.github.com/en/actions/hosting-your-own-runners/managing-self-hosted-runners/running-scripts-before-or-after-a-job#triggering-the-scripts
+cat <<EOT > ./actions-runner/start-hook.sh
+#!/bin/sh
+printenv | grep GITHUB > /home/runner/actions-runner/.github_context
+EOT
+chmod +x ./actions-runner/start-hook.sh
+
+echo "ACTIONS_RUNNER_HOOK_JOB_STARTED=/home/runner/actions-runner/start-hook.sh" | sudo tee -a /etc/environment
+
 # runner script doesn't use global $PATH variable by default. It gets path from
 # secure_path at /etc/sudoers. Also script load .env file, so we are able to
 # overwrite default path value of runner script with $PATH.