Update and fix docs

[svenvg93]

• Fixes the Traefik docs not showing to close Traefik config missing in Gitbook #29
• Remove the env form the installation and fix the link to the env page to close Combine "installation" and "environment variable" lists #30 and close environment-variables link not working #33
• Update the frontage image, as one of the comments was it wasn't updated after removing the General page. ¯_(ツ)_/¯
• Removed the "service 3.4" from all the docker compose files as it is not mandatory anymore.
• replace the latest tag in the docker compose with the last version and link to the LSIO page for the latest version