RestHighLevelClient - Default Index and Type should be supported in BulkRequest

[koalalam]

When calling bulk/bulkAsync function in RestHighLevelClient, the parameter BulkRequest doesn't support default index and type which is supported in the Bulk API:

https://www.elastic.co/guide/en/elasticsearch/reference/6.2/docs-bulk.html

"The endpoints are /_bulk, /{index}/_bulk, and {index}/{type}/_bulk. When the index or the index/type are provided, they will be used by default on bulk items that don’t provide them explicitly."

However, when BulkRequest is converted to Request object, only "/_bulk" is used.

This is important if url based entitlement is used and "rest.action.multi.allow_explicit_index" is set to true

https://www.elastic.co/guide/en/elasticsearch/reference/6.2/url-access-control.html

Elasticsearch version (bin/elasticsearch --version): 6.x

Plugins installed: []

JVM version (java -version): 1.8

OS version (uname -a if on a Unix-like system): Linux

[elasticmachine]

Pinging @elastic/es-core-infra

[javanna]

This is the same problem as described in #26026 . Closing in favour of the existing issue.