[Discover] Aggregate metric field columns display oddly in Discover

[davismcphee]

When adding an aggregate metric field as a column to the Discover table, it displays oddly.

It displays reasonably in the Summary column:

But not as an individual column:

The issue seems to be a combination of two things:

• We auto format the JSON for object field values when added as a column.
• We right-align number field values when added as a column, and aggregate metric fields seem to have type: number.

Together this causes it to render as right-aligned and JSON formatted, which doesn't really work.

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)