Allow non-indexed fields to be referenced in creation of Alerts visually.

[crackthecodeabhi]

I have observed that, if a field is not indexed/searchable, then i cannot choose that field when i try to create alert visually which aggregates over a field. But if i make it indexed/searchable, then i can select that field.

For logs visualization and alerting, we disable source fields, hence we cannot create alerts based on the fields.
It is possible in Watchers, to create alerts using non-indexed fields.

Please make this possible with Alerting also.

Thanks.