add tester account to api key issuers example

Author: jamalc

src/webapp/.env.example

@@ -32,4 +32,4 @@ DATABRICKS_HOST_URL=""
 DATABRICKS_SERVICE_ACCOUNT_EMAIL=""
 
 # Datakinders allowed to issue API key. This should be the MINIMUM set. Keep this group small. Pass as a comma separated string structured like so: "abc@dk.org,bcd@dk.org"
-API_KEY_ISSUERS=""
+API_KEY_ISSUERS="tester@datakind.org"