TermsSetQuery should support boost field

[TakiuGit]

TermsSetQuery misses the boost field :
https://github.com/sksamuel/elastic4s/blob/master/elastic4s-domain/src/main/scala/com/sksamuel/elastic4s/requests/searches/term/TermsSetQuery.scala

It's shown as an example in the documentation but not listed explicitly in the parameters (see last example):
https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-terms-set-query.html