core (xmpp): make `send` a blocking method, fix `sendMessageData` calls: original `send` method is blocking, and it is used as such by Wokkel and thus can't be changed to an async method easily. However, an Async method is necessary to have an async trigger at the very end of the send workflow for end-to-end encryption. To workaround that, `send` is an async method which call `a_send`, an async method which actually does the sending. This way legacy method can still call `send` while `a_send` can be await otherwise. Fix calls to `sendMessageData`: the method now being an `async` one, `ensureDeferred` had to be used in some calls.

[DEFAULT]
xmpp_domain = server1.test
email_server = libervia-backend.test
email_port = 8025
email_admins_list = admin@server1.test

[component file-sharing]
http_upload_public_facing_url = http://localhost:7777
http_upload_connection_type = http
http_upload_port = 7777