Utilizing 0.0.0.0 IP for API URL is not proxy friendly

[Drew Freiberger]

Using the address 0.0.0.0 for talking to the API within the graylog charm is not conducive to being able to pass through a proxy or set in NO_PROXY.

When the graylog charm goes to talk to the graylog api via http://0.0.0.0:9001/ it fails because it hits the proxy config, even when 127.0.0.1/localhost/PublicIP are configured in the NO_PROXY environment variable.

While the graylog API may need to listen on 0.0.0.0 to open all interfaces, the URL 127.0.0.1 should be used for internal graylog charm to API communication.