add config validator subcommand (#80)

* add config validator subcommand

* add --exit-code flag

* docs & faq update

docker/entrypoint.sh

@@ -47,6 +47,9 @@ if [ -n "$AHRIMAN_UNIX_SOCKET" ]; then
 fi
 ahriman "${AHRIMAN_DEFAULT_ARGS[@]}" repo-setup "${AHRIMAN_SETUP_ARGS[@]}"
 
+# validate configuration if set
+[ -n "$AHRIMAN_VALIDATE_CONFIGURATION" ] && ahriman "${AHRIMAN_DEFAULT_ARGS[@]}" repo-config-validate --exit-code
+
 # create machine-id which is required by build tools
 systemd-machine-id-setup &> /dev/null