Simplify running with podman

Allow to adjust the docker socket path used by traefik and the logging driver
so that this example can be more easily used with podman based setups.

With a running podman service ("podman system service --time 0"), this should
basically work:

export DOCKER_SOCKET_PATH="/run/user/1000/podman/podman.sock"
export LOG_DRIVER=journald
docker-compose -H unix:///run/user/1000/podman/podman.sock up

deployments/examples/ocis_keycloak/docker-compose.yml

@@ -33,7 +33,7 @@ services:
       - "80:80"
       - "443:443"
     volumes:
-      - "/var/run/docker.sock:/var/run/docker.sock:ro"
+      - "${DOCKER_SOCKET_PATH:-/var/run/docker.sock}:/var/run/docker.sock:ro"
       - "certs:/certs"
     labels:
       - "traefik.enable=${TRAEFIK_DASHBOARD:-false}"
@@ -44,7 +44,7 @@ services:
       - "traefik.http.routers.traefik.tls.certresolver=http"
       - "traefik.http.routers.traefik.service=api@internal"
     logging:
-      driver: "local"
+      driver: ${LOG_DRIVER:-local}
     restart: always
 
   ocis:
@@ -81,7 +81,7 @@ services:
       - "traefik.http.routers.ocis.service=ocis"
       - "traefik.http.services.ocis.loadbalancer.server.port=9200"
     logging:
-      driver: "local"
+      driver: ${LOG_DRIVER:-local}
     restart: always
 
   postgres:
@@ -95,7 +95,7 @@ services:
       POSTGRES_USER: keycloak
       POSTGRES_PASSWORD: keycloak
     logging:
-      driver: "local"
+      driver: ${LOG_DRIVER:-local}
     restart: always
 
   keycloak:
@@ -129,7 +129,7 @@ services:
     depends_on:
       - postgres
     logging:
-      driver: "local"
+      driver: ${LOG_DRIVER:-local}
     restart: always
 
 volumes: