* made a few changes in order to further simplify the setup for
developers of the Groupware backend
* add STALWART_DOMAIN to deployments/examples/opencloud_full/.env
* adapt the Stalwart configuration file to not set server.hostname and,
instead, pick it up from /etc/hostname, which is set by Docker
Compose as we can use default values for STALWART_DOMAIN there, in an
analogous fashion to the other containers in that project
* add config/keycloak/clients/groupware.json to avoid requiring manual
configuration of Keycloak via the admin web UI
* Stalwart container:
- listen for SMTPS on :1465
- remove the stalwart-logs volume, not needed (logs are going to
stdout)
* updated services/groupware/DEVELOPER.md:
- refer to a variable OCDIR to make instructions more copy-pasteable
- remove manual Keycloak configuration section as it is now obsolete,
replaced by provisioning a configuration file instead
