Add warning for infinite values in a range aggregation

[alexfrancoeur]

When building a visualization that uses a range aggregation, an empty value is an infinite value. This is not obvious to all users. It'd be nice to provide a warning for empty values letting the user know that they're about to query to +/- infinity.

[elasticmachine]

Pinging @elastic/kibana-app

[timroes]

I would suggest we just use -∞ and +∞ as a placeholder for the from respective to box. So if the user doesn't enter anything in there, they see that it will default to that value. @maryia-lapata @sulemanof Maybe we could address that when moving over the Range control over to React in the same step?

[maryia-lapata]

@timroes yes, of course, we will address this issue during Range control migration.