Add `scaled_float` numeric type support

[ebeahan]

Add support in ECS for scaled_float as an allowed numeric type in the schema field definitions.

A scaled_float has an additional parameter, the scaling_factor. scaling_factor is always required for a scaled_float.

{
  "my-index-0002" : {
    "mappings" : {
      "properties" : {
        "my_scaled_float_field" : {
          "type" : "scaled_float",
          "scaling_factor" : 1000.0
        }
      }
    }
  }
}