Simply environment variable management

[mlhaufe]

There is currently significant duplication in the managing of the environment variables:

.env file
Four reference in azure-deploy.yml
Two references in main.bicep
Two references in appService.bicep
One reference in github secrets.

Try to leverage the .env file as much as possible and drop the app service references. I think the .env file will be used if it's deployed to the root.