[Metrics UI] P95/P99 charts not rendering in Metrics Explorer and Alerts throws exeception

[simianhacker]

Kibana version:
master, 7.8
Elasticsearch version:
master, 7.8
Describe the bug:
When you render a chart with either 95ty Percentile or 99th Percentile the charts are empty. When you create an alert from the Metrics Explorer UI using percentiles the Alerts dialog throws an exception

Steps to reproduce:

1. Open Metrics Explorer
2. Set aggregation to 95th percentile
3. Notice no data in the charts
4. Click on "Actions" and "Create alert"
5. BOOM!

Expected behavior:

It should render data and not throw the exception in alerts

Screenshots (if relevant):

Alerts Error

[elasticmachine]

Pinging @elastic/logs-metrics-ui (Team:logs-metrics-ui)