Create ZLUX server.json containing defaults for container start

[markjhollands]

Currently, the values for the TLS certificates are specified in the docker-compose.yml file as environment variables, as follows:

services:
    zlux-app-server:
        environment:
            ZWED_node_https_keys: "/tls/tls.key,"
            ZWED_node_https_certificates: "/tls/tls.crt,"
            ZWED_node_https_certificateAuthorities: "/tls/ca.crt,"

As these values are automatically configured by other parts of the configuration they are unlikely to change, and could even be accidentally changed by a user.

These values should be configured in a default server.json file, and only values like agent hostname (ZWED_agent_host) should be overridden as environment variables.

[markjhollands]

Note: the environment variable method for the certs is also prone to error. This is because if there is a single cert (as in the description), a user must include a trailing comma for the config to be parsed as an array.