add env_vars nobuild

joplin/config.yaml

@@ -73,6 +73,7 @@ map:
   - share:rw
 name: Joplin Server
 options:
+  env_vars: []
   APP_BASE_URL: http://your_domain:port
   data_location: /config/addons_config/joplin
 ports:
@@ -82,6 +83,9 @@ ports_description:
 privileged:
   - SYS_TIME
 schema:
+  env_vars:
+    - name: match(^[A-Z0-9_]+$)
+      value: str?
   APP_BASE_URL: str
   DB_CLIENT: str?
   MAILER_AUTH_PASSWORD: str?