[Filters] Add support for creating regex filters

[Jolter]

Describe the feature:

As a user, I want to add a Filter to my search using a regex matching Operator in the "Add filter/Edit filter" dialog , so that I can do regex matching without using the Lucene/KQL search box.

I imagine that this dropdown would be extended with an additional Operator called "matches". (Other suitable name suggestions might be "matches regex", or insert your suggestion here.)

A related change is labeled for v8.1.0, where a Registry is added for these values. #111897
I wouldn't mind seeing this feature in v7.X, but v8.X would also be fine.

Describe a specific use case for the feature:

Target users are beginner Kibana users who are unlikely to become experts, i.e. users unwilling to invest time in learning KQL or Lucene search syntax, where the regex functionality already exists.

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServicesUx)

[lukasolson]

@Jolter, agreed that this would be a nice addition. Until it's added, as a workaround you can click "Edit as Query DSL", and then enter something like the following:

{
  "query": {
    "regexp": {
      "username": {
        "value": "k.*y",
        "case_insensitive": true
      }
    }
  }
}

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[Kalocjak]

Definitely a desirable feature. Something that would look like this - option to select between match_phrase, wildcard, regexp, regexp (case insensitive) would make searching much quicker and more comfortable.

[kertal]

Closing this because it's not planned to be resolved in the foreseeable future. It will be tracked in our Icebox and will be re-opened if our priorities change. Feel free to re-open if you think it should be melted sooner.

When using ES|QL in Kibana it's already possible to make use of RexExp e.g. by using RLIKE
https://www.elastic.co/guide/en/elasticsearch/reference/current/esql-functions-operators.html#esql-rlike-operator