Provoked by https://github.com/mother-of-all-self-hosting/mash-playbook/pull/280

* Add upstream `proxy_protocol` instructions to traefik

* Fix YAML indentation to use spaces

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Co-authored-by: Slavi Pantaleev <slavi@devture.com>

* Update configuring-playbook-traefik.md

Added docu on how to host another server behind traefik.

* Added MASH and docker options

Added the link to mash and the compatibility adjustments.

Mentioned the prefered method with docker containers.

Some rephrasing to make clear, the intended guide ios for reverse proxying non-docker services.

* Improve wording in configuring-playbook-traefik.md

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Co-authored-by: Slavi Pantaleev <slavi@devture.com>