[Lens] Field existence doesn't work on epoch_millis dates

[flash1293]

Kibana version: 7.15

Describe the bug: Similar to #119444, field existence fails if epoch_millis dates are used for the default time field of the index pattern

Steps to reproduce:

PUT /test
{
  "settings" : {
    "index" : {
      "number_of_shards" : 1,
      "number_of_replicas" : 0,
      "refresh_interval" : "1s"
    }
  },
  "mappings" : {
    "dynamic" : "strict",
    "date_detection" : false,
    "properties" : {
      "timestamp" : {
        "type" : "date",
        "format" : "epoch_millis"
      }
    }
  }
}
POST test/_doc/
{
  "timestamp": 1636749579080
}

Any additional context:

This is happening because the filter building logic is not setting the "format": "strict_date_optional_time" property of the range filter.

Right now the only workaround is to only use time shift with strict_date_time dates.

kibana/x-pack/plugins/lens/server/routes/existing_fields.ts

Line 186 in 1ac885e

gte: fromDate,

#119444