feat: Add multi-target load balancing support

Fixes #47.
- Added lua-resty-balancer to dependencies (Dockerfile & install.sh).
- Added 'targets' field to the Host model to hold additional targets.
- Updated the UI to allow inputting additional targets (IP:port).
- Updated targetinfo.lua to parse the additional targets and load balance between them and the primary target using resty.balancer.round_robin.

nodejs/models/host.js

@@ -28,6 +28,7 @@ class Host extends Table{
 		'host': {isRequired: true, type: 'string', min: 1, max: 500},
 		'ip': {isRequired: true, type: 'string', min: 3, max: 500},
 		'targetPort': {isRequired: true, type: 'number', min:0, max:65535},
+		'targets': {default: function(){return []}, isRequired: false, type: 'object'},
 		'forcessl': {isRequired: false, default: true, type: 'boolean'},
 		'targetssl': {isRequired: false, default: false, type: 'boolean'},