Dockerized launching mkdocs server

[alongosz]

Question	Answer
JIRA Ticket	n/a
Versions	4.6, 5.0
Edition	All editions

This PR adds Dockerfile and compose.yaml configuration for docker compose to launch the Documentation page locally by simply stating:

docker compose up --watch

You can launch it also in a detached mode:

docker compose up -d

but then any local changes to the doc won't be reloaded.

By default it will launch mkdocs server at http://0.0.0.0:8000/en/latest/

To use different port (since 8000 can be already occupied by e.g., Symfony dev server), before running docker compose, run:

export MKDOCS_PORT=8888

where 8888 is the desired port.

The main pain point right now is that on Ubuntu python packages are externally managed and doing pip -r requirements.txt is not going to work OOTB.

Known issues

I'm not able to make mkdocs server automatically reload after changes, regardless of if I use --watch or --dirty option. As a workaround, docker will restart the service after any changes. The restart is triggered after about ~10 seconds and it takes extra ~20 seconds to rebuild the server.

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