Move anonymous credentials secret key to parameter store

[LDiazN]

We want to move the manifest for anonymous credentials to a versioned and publicly available s3 bucket

The public parameters are part of the manifest. It's a string that works like a public key, bound to a secret key

The task is to move the storage of this secret key to parameter store, instead of storing it in the database

[LDiazN]

closed by #308