[Feature Request] Port forwarding to Login nodes from the Load Balancer

# Currently

PCluster creates for login nodes (pools) an Elastic Load Balancer (NLB) with:
- A target group encompassing the login nodes for Port 22, TCP
- A listener for port 22, TCP

# Request

Enable customization for this. For each [pool](https://docs.aws.amazon.com/parallelcluster/latest/ug/LoginNodes-v3.html#LoginNodes-v3-Pools) add the key "LoadBalancers" is a list of "LoadBalancer", having two keys "Type" and "PortForwardings". "Type" is either ALB or NLB for the type of load balancer. PortForwardings is a list of a "Portfowarding" class, having the keys:
- SourcePort, Integer, Required, Constraint: >= 0
- TargetPort, Integer, Required, Constraint: >= 0
- Protocol, String, Required, Constraint: [TCP, UDP]
- Certificate: String, optional, Constraint: ARN of certificate in ACM, default: None
- Stickiness: Boolean, optional, default: false

With those information, PCluster will set up the target groups and listeners, populated with the values provided.

Start by reviewing how PCluster currently creates the login-node pools' network load balancer, target group, and port-22 listener. Then trace the login-node pool configuration entry point and determine how the requested LoadBalancers and PortForwardings fields should map to ALB/NLB target groups and listeners; done means the documented options create the requested forwarding configuration with the stated validation and defaults.

Written by the indexing model from the issue text.