Validate `type` property for `chart-series-label` component, update stories accordingly

The following discussion from !2522 (merged) should be addressed:

• @ohoral started a discussion:

  thought: it looks like we support only two types solid and dashed. So given that, I believe we can make type control to be of select type and allow only those 2 values. But first, we need to add validation to the component porperty so this is a bit out of scope.