Add CLOUDRON_MAIL_SMTP_STARTTLS env

starting 6.3, the internal mail server will do STARTTLS. this env
allows apps to configure themselves appropriately for pre 6.3 and
post 6.3 appropriately.

we trigger a re-configure which ensures that the new env gets put
in the database and then in the container.

src/infra_version.js

@@ -6,7 +6,7 @@
 
 exports = module.exports = {
     // a version change recreates all containers with latest docker config
-    'version': '48.18.0',
+    'version': '48.19.0',
 
     'baseImages': [
         { repo: 'cloudron/base', tag: 'cloudron/base:3.0.0@sha256:455c70428723e3a823198c57472785437eb6eab082e79b3ff04ea584faf46e92' }