Refactor env.templates

I realized, that the following step in the read.me requires some more steps, then just copy the file:

Copy all files ending with env.template. Fill the variables and rename it to env.dev

The steps in the readme should be doable by someone new to the project (e.g. me yesterday 😖 ). This means they should be simple and complete

We should

Create one default-template.env (containing only the vars that are currently used by every setup)
Create a ufz-setup-template.env
Create a gfz-setup-template.env
Any optional env-blocks should be possible to comment/uncomment by an IDE like VS-code, sublime,... by marking the block. Avoid something like the code block below
( Optional ) put the files in an extra folder?
Adapt the gitignore.
Adapt the readme line. Expecially include a hint, that die client-id should be pasted into one of the files.

Yes the files should end on .env and not template, so that an IDE code highlighting works ect.

Ugly to uncomment:

## GFZ
# GFZ IDP
# WELL_KNOWN_URL=https://login-dev.helmholtz.de/oauth2/.well-known/openid-configuration
# OIDC_USERDATA_IDENTITY_CLAIM eduperson_principal_name
# Client ID (Audience)
#OIDC_CLIENT_IDS=backend