Copy ENVIRONMENT.md into the ownCloud config/ folder to be part of the image

[mmattel]

References: #472 (fix: add memory_limit and LimitRequestBody for big file upload support)

When reading the change of the referenced PR (much appreciated), I saw that there is a file named ENVIRONMENT.md where (hopefully) all envvars for a Dockerised ownCloud installation are present. Because I do not want to reinvent the wheel creating such a list in the docs, I propose the following change:

• Copy the ENVIRONMENT.md file into the config folder of ownCloud, there where config.php / overwrite.config.php is located.
  Because this folder is part of the Docker mounted volume, one can easily access and read it. Note that ownCloud only reads .php files in this folder which means adding an .md file does no harm.

• As a second task, we need to check if there are envvars missing and add them if so.

• Finally, we should check the sorting of keys. This is because I have found at least one out of order.
  OWNCLOUD_IOC_SCANNER_CONFIRMATION is in last position and not where it is expected.

Benefit
One place to maintain available envvars which is a huge impact for docs

@DeepDiver1975

[DeepDiver1975]

the environment.md file belongs to the docker image and has to be maintained in the same repo - keep it simple for maintainers

likewise this file has nothing to do with the core repo - wrong location as well

all individual components need to be pulled together in the docs - this is understood ..... will look for a solution ....

[DeepDiver1975]

actually this will be a one time action for the documentation - either do it manually or use claude

[mmattel]

I disagree on closing without a long term solution.

• From a customers perspective, this info needs to be present
• The data is already present in a fully functional and admin readable form.
• From a docs perspective, it is pointless not having that file being part of the config folder, whatever repo this is added.
  Any change on that file hands over responsibility of maintenance to docs and will result in loss of info because docs is and will not maintain this information and keep it in sync.