Disagg IML: Handle Service Call

Requires #121 (closed)

Update service call effect to call the IML or return period disagg service based on the DisaggTarget:

• Add switch statement on values.disaggTarget to construct the url that will be called
• Add default case that throws an error with message Disagg target [${disaggTarget}] not supported
• Updated control validator to only validate IML if DisaggTarget is IML and only validate return period if DisaggTarget is RETURN_PERIOD

IML service call example: disagg/-80/40/760?PGA=0.125&out=GMM&out=SOURCE&out=DISAGG_DATA

switch (values.disaggTarget) {
  case DisaggTarget.IML: {
    url = '';
    break;
  }
  case DisaggTarget.RETURN_PERIOD: {
    url = '';
    break;
  }
  default:
    throw new Error()
}

See main issue for bigger picture: #93 (closed)