* Prometheus: Add off switch for metric/label name lookup

This will help users with amounts of metric name
data that is too much for a browser to handle.

Autocomplete will be disabled and metrics chooser hidden,
since obviously both rely on this data.

Fixes #22702

* Use onUpdateDatasourceJsonDataOptionChecked

... from `@grafana/data`. Refactor naming to faciliate its
use and stick with prop names as passed down from
`ConfigEditor`.

PLUS:
- Rephrase switch label, add a tooltip and reduce the
size of the to what "Custom query parameters" originally
was.
- Change `languageProvider` type in `PromQueryField`.

* Put language provider back in

Functions and history still work, even when metrics
lookup gets disabled.
Also: Rewording of setting.

* Display a message when lookup got disabled manually

* Call property for setting disableMetricsLookup

* Show disabled metrics chooser instead of warning