Added settings needed for reverse proxy setup

[HaraldWilhelmi]

We need to put our SODAR installation behind another reverse proxy. For this purpose we exposed some more Django settings via environment variables. A word of warning about the general topic:

• The present, official Django documentation states that CSRF_TRUSTED_ORIGINS should be a list of URL patterns (e.g. 'https://*.example.com').
• The Django version presently used in our SODAR container (3.2.24) uses domain names or domain name suffixes (e.g. '.example.com' or 'sodar.example.com'). That I learned by reading the source.

So a upgrade of the Django version used may change that.

[HaraldWilhelmi]

Thanks for the feedback. Will re-file a pull request with changes and a ticket.