New ENV vars when introducing Kratos to secure the Admin UI

[JoblersTune]

New env variables in the admin containers:

• LOG_LEVEL: defaults to info
• NODE_ENV: has no default. It is only used as a check to determine whether the logs should be in pretty print for dev environments.
• KRATOS_CONTAINER_PULIC_URL: required for frontend package, no default values. This is the public Kratos endpoint in the form for a browser to understand.
• KRATOS_BROWSER_PUBLIC_URL: required for frontend package, no default values. This is the public Kratos endpoint in the form for the admin container to understand.
• KRATOS_ADMIN_URL: required to run user invitation script etc, no defaults. This is the admin Kratos endpoint in the form for a container to understand, since the admin endpoint should not be exposed.

New env variables in the kratos containers:

• PATH_TO_KRATOS_CONFIG: is a Docker build arg to point to the kratos.config file that should be used.
• DEV_MODE: used in the entrypoint script for running the kratos container to determine whether startup should be in dev mode or not.

See PR interledger/rafiki#2588

[JoblersTune]

@tadejgolobic SIGNATURE_VERSION (1) and SIGNATURE_SECRET (undefined) have also been added.

[JoblersTune]

We also need to add in AUTH_ENABLED environment variable for Rafiki Admin. It defaults to true.