Improve environment variables documentation for docker

[nck974]

How did you install WebODM (docker, installer, etc.)?

Docker
What's your browser and operating system? (Copy/paste the output of https://www.whatismybrowser.com/)
Windows 11

What is the problem?
To keep organized the multiple containers I used some custom names for the container names instead of the default ones used in the docker-compose.yaml. During the first installation I had many problems to find out out to configure the domain names of multiple services which seem to be also duplicated.

The following were the examples I found:

1. WO_DATABASE_HOST: I could only find this setting from the code, this same settings seems to be used in the docker-compose.yaml directly as parameter /webodm/wait-for-postgres.sh <container_name>. Would it make sense to just use one environment variable for all in the .env?
2. WO_BROKER: This one can be fund directly in the .env, but it is also duplicated, for example in: /webodm/wait-for-it.sh -t 0 opendronemap_broker:6379. Would'T it also make sense to somehow unify it?
3. WO_DEFAULT_NODES: I could not find at first glance what does this variable do, I was also not able to configure a node automatically through environment variables without having to configure the host manually in the UI. Is this possible and not documented or is a step that must always be done?

I was able to get WebODM running but took me some time, to debug those issues, maybe this documentation would save someone else in the future. I would have sent a PR but I'm not sure on howw/where is the place to document this things,

How can we reproduce this? (What steps trigger the problem? What parameters are you using for processing? Include screenshots. If you are having issues processing a dataset, you must include a copy of your dataset uploaded on Dropbox, Google Drive or https://dronedb.app/)
Not applicable as it is a documentation isse.