The Java API documentation for index administration currenty is wrong because
the PutMappingRequestBuilder#setSource(Object... source) and
CreateIndexRequestBuilder#addMapping(String type, Object... source) methods
delegate to methods that check that the input arguments are valid key/value
pairs:
https://www.elastic.co/guide/en/elasticsearch/client/java-api/current/java-admin-indices.html
This changes the docs so the java api code examples are included from
documentation integration tests so we detect compile and runtime issues earlier.
Closes#28131