Prometheus: Improve autocomplete performance and remove disabling of dynamic label lookup (#30199)

* processLabels: Use Sets instead of Array

* Add and update comment

* Limit autocomplete items to 10000

* Remove lookup treshold, limit display of items

* Update tests

* Add test

* Update public/app/plugins/datasource/prometheus/language_provider.ts

public/app/plugins/datasource/prometheus/components/PromQueryField.tsx

@@ -209,9 +209,9 @@ class PromQueryField extends React.PureComponent<PromQueryFieldProps, PromQueryF
     let hint = hints.length > 0 ? hints[0] : null;
 
     // Hint for big disabled lookups
-    if (!hint && !datasource.lookupsDisabled && datasource.languageProvider.lookupsDisabled) {
+    if (!hint && datasource.lookupsDisabled) {
       hint = {
-        label: `Dynamic label lookup is disabled for datasources with more than ${datasource.languageProvider.lookupMetricsThreshold} metrics.`,
+        label: `Labels and metrics lookup was disabled in data source settings.`,
         type: 'INFO',
       };
     }