Group other values doesn't work for scripted fields

[lukasolson]

Describe the bug:

The "group other values in a separate bucket" option doesn't work for scripted fields.

Steps to reproduce:

1. Create a scripted field
2. Create a data table visualization
3. Split rows using a terms aggregation on the scripted field
4. Select to group other values in a separate bucket

Expected behavior:

The other bucket would work, even with scripted fields.

Screenshots (if relevant):

Any additional context:

In looking at the query generated for the "other bucket", it adds an exists query on the scripted field. Of course, since the scripted field itself doesn't exist in the index, this will filter out all of the hits. I'm not sure if that exists query is necessary for regular fields, but we need to remove it for scripted fields:

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)