Forbid specifying the same percentile multiple times

[timroes]

With elastic/elasticsearch#52257 Elasticsearch removes the ability to specify the same percentile value multiple times in a percentile aggregation. This will go into 8.0 since it's a breaking change. We should make sure we're also not allowing the user to specify two times the same percentile value in the visualize editor, since otherwise that request would start failing and the user doesn't have a clear error anymore what's happening. Instead the editor should show a clear error message on that, and make sure we can't save that state.

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)