Add FORWARDED_FOR_HEADERS to the reverse-proxy config

[dgiebert]

Description of the change

With the new proxy config added, I want to be able to remove all manual config in the helm chart and use env vars

Not sure this needs a new version, can be added to the next bigger release imo

Checklist

• [x] I have read the CONTRIBUTING.md doc.
• [x] DCO has been signed off on the commit.
• [ ] Chart version bumped in Chart.yaml according to semver.
• [ ] (optional) Parameters are documented in the README.md

[provokateurin]

We're just using the config from https://github.com/nextcloud/docker/blob/master/.config/reverse-proxy.config.php and try to stay in sync with it, so I'd prefer if it was submitted there first since the maintainers of the docker image will know if this makes sense. After that we can just add it here by updating the file from upstream. @jessebot what do you think about this process?

[jessebot]

@provokateurin yeah, that makes sense to me. I think trying to keep in sync with the docker repo is ideal, because then we can also better collaborate across repos.

The only downside is that we're both, nextcloud/helm and nextcloud/docker, on different release cycles, so the docker image may take a month or two to merge something, which can sometimes mean we won't be able to merge that same thing for at least that amount of time.

[dgiebert]

Then I will go ahead and create a PR against nextcloud/docker and reference it here.

[jessebot]

Thank you, @dgiebert ! 🙏