[ES|QL] Document ES|QL support for the Elasticsearch input

### Documentation
- `event.original` isn’t available when response type is ES|QL
- `query` param to accept ES|QL query and examples
- `response_type` to accept new `esql` value and notice to
- deprecate in the future, will be replaced by `query_type`
- for the es-filter, `esql_params` with examples
- any limitations
- error cases
