Add healthchecks for all Taiga services, fix RabbitMQ env var names, and define TAIGA_HOSTNAME

Details:
- Implemented healthchecks for taiga, async, rabbitmq, front, events, protected, and gateway
- Corrected RabbitMQ env variables (RABBITMQ_DEFAULT_USER/PASS/VHOST/ERLANG_COOKIE)
- Added TAIGA_HOSTNAME for backend service

See: https://chatgpt.com/share/68da9d6b-b164-800f-bcb7-410b40219a1e

roles/web-app-nextcloud/config/main.yml

@@ -54,8 +54,8 @@ docker:
       backup:
         no_stop_required:   false
       turn_server:
-        onboard_enabled:    true
-        standalone_enabled: true
+        onboard_enabled:    true # Deactivated because standalone turnserver works with  Big Blue Button, so I assume that the nextcloud internal turnserver has it's isssues
+        standalone_enabled: false
       network_mode:         host
     whiteboard:
       name:                 "nextcloud-whiteboard"