entity 'mentions' feature is not available via Discovery tooling

[rhagarty]

This feature is only available using the Disco API, so users loading their own data sets and config using the Discovery UI tooling won't have access to this.

To get this feature, they can need to let the app build the data for them.

This 'feature' adds a couple of nice enhancements to the app UI:

1. if the user selects an 'entity' filter, the 'entity' will be highlighted in the AirBnb review text.
2. if the user selects an 'entity.type' filter, any corresponding matches will be highlighted in the AirBnb review text. For example, if they select the 'entity.type' filter of "Sport", "golf" and "baseball" will be highlighted.