[ES|QL editor in Kibana] Full text search & recommendation

[florent-leborgne]

See elastic/kibana#221239
also elastic/kibana#220691

After looking into this, I think release notes are sufficient for kibana as this comes from a general ES|QL language improvement (not specific to kibana)
That said, we need to make sure that ES|QL Kibana docs properly link to the ES|QL syntax docs when needed