Phabricator updated configuration format for mailer, to use a JSON document.
An example for Mailgun is the configuration for DevCentral:
[ { "key": "nasqueron-mailgun", "type": "mailgun", "options": { "domain": "devcentral.nasqueron.org", "api-key": "key-00000000000000" } } ]
We need to generate such document from environment variables in the setup container script,
then provide it using ./bin/config set --stdin cluster.mailers < /tmp/mailers.json
Key could be "default-<mailer type>".