This is the relevant branch config (non-top-pick) from [the final Yelp v3 experiment](https://experimenter.services.mozilla.com/nimbus/yelp-suggestions-pilot-v3/summary)
that we should now make the default:
```json
{
"yelpFeatureGate": true,
"yelpSuggestPriority": false,
"yelpShowLessFrequentlyCap": 3,
"yelpMinKeywordLength": 4,
"exposureResults": "rust_yelp",
"showExposureResults": true
}
```
Ideally we might define `minKeywordLength` as part of the Yelp data in remote
settings and then modify the Rust component to ingest it as Yelp config data,
similar to weather suggestions. But that would require modifying the Rust
component, and Product wants Yelp for 129, so that means we would need to uplift
a vendoring of application-services to Beta, which I think we should avoid.
So instead I just set the default value of the `minKeywordLength` pref to 4. I
kept the Nimbus variable and it will override the pref if the pref still has its
default value. That way we can still use Nimbus to set it if there's some
emergency.
I also kept the `yelpSuggestNonPriorityIndex` and `yelpSuggestPriority`
variables, in case we need those too. Eventually we should clean up all the
variables and prefs we're not using anymore.
Differential Revision: https://phabricator.services.mozilla.com/D215709
6d0d1ba5c9