Support multi match type 'bool_prefix'

[wolfsblu]

Adds support for the multi match query type bool_prefix [1]

[1] https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-multi-match-query.html#multi-match-types

[ruflin]

Thanks for the contribution. Could you add an entry to the Changelog file? And can you check the tests if there is a way to add one to make sure it works with different Elasticsearch versions?

[wolfsblu]

Added changelog and test case

[ruflin]

Thanks for the contribution!