Extend model_settings file with a loss_factor section

[sambles]

Issue Description

The feature OasisLMF/OasisLMF#1558 allows for multiple PLA files to be defined on a model. But there is no place in the model_settings file to put these.

Expectation would be that it follows a similar format to event_set or event_occurrence

{
    "model_settings":{
        "lossfactor_set":{
            "name": "Lossfactor Set",
            "desc": "Lossfactor Set,
            "default": "10k",
            "options":[{
                "id": "1k",
                "desc":"1k"
            },{
                "id": "10k",
                "desc":"10k"
            }]
        },
        "event_set":{
            "name": "Event Set",
            "desc": "Event Set",
            "default": "10k",
            "options":[{
                "id": "1k",
                "desc":"1k"
            },{
                "id": "10k",
                "desc":"10k"
            }]
        },
          ...

[sambles]

dup of #148 closing this issue