🔧 read cognito values from environment variables instead of a file

[shankari]

If the values have to be read from a file, then, in a multi-tenant environment, we will need separate images for each tenant.
The whole point of the dynamic config is to avoid that - so that we can reuse the same docker image for all tenants.
We cannot put the cognito values into the dynamic config for obvious reasons, but we can and should put it into environment variables so that we can configure different instances of the image correctly.

[shankari]

I have a partial fix checked in for now.
927817a

However, we should think about this carefully and clean it up a bit.
For example, we might want to reconsider whether we even need to read cognito values from a file given that we are going to support environment variables anyway.