metricName type description

[peterpeterparker]

Hi 👋

Thanks for the great library!

I noticed that the information metricName of IAnalyticsTrackerOptions wasn't stricly typed and defined as string. I'm not sure if there's a particular reason for this, but if not, I think it would be helpful to strongly type it. At least for me, as someone discovering and starting to use the library, this would have been helpful.