[KQL] [Filter editor] Cancel discarded requests for suggestions

[lukasolson]

When a user is typing KQL, and types something along the lines of field: , we start to suggest values for that particular field. To suggest values, we make a request to Elasticsearch and do a terms query for the suggestions. For each keystroke, we make a new request, but we never end up cancelling the previous requests, which means the burden remains on Elasticsearch.

The same can be said when a user opens the filter editor and selects a field, then the is or is one of operator and begins typing in the value text input.

We need to cancel previous requests in the following scenarios:

1. When the user navigates away before the search completes
2. When a new search is requested before the prior one completes

[elasticmachine]

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

[lukasolson]

Related: #46054

[lukasolson]

Reopening. Requests are being cancelled in the second scenario, but not when users navigate away.