Updated kpi-overview top bar fetch to use params

[ErisDS]

ref https://linear.app/tryghost/issue/ANAL-67/audience-filtering-doesnt-update-the-top-metrics-just-the-charts

• At the moment we are manually fetching the top bar data for KPIs via Ember.
• This was done quickly, and didn't make use of the params for audience or chartRange
• We need these params to fetch filtered data results