chore: add support for feature toggle for health diagnostics

[vickyyyyyyy]

Add support for toggling our healthDiagnosticsErrorsCompat return.

This is because for the new health diagnostic error messages, we are planning to beta release them first so we want them to be switched off by default.

Usage in our plugins:

import { healthDiagnosticsErrorsCompat } from 'ui-enterprise';
import toggles from './featureToggles';

async testDatasource() {
    return healthDiagnosticsErrorsCompat(super.testDatasource.bind(this), toggles.healthDiagnosticsErrors);
}

[yesoreyeram]

LGTM