NIFI-3140: Restored optional type handling in FetchElasticsearchHttp

[mattyb149]

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[mattyb149]

@gresockj Do you mind taking a look at this? I want to make sure I didn't miss something in the API or any potential differences between versions. For the Http processors I'd like to keep the least-common-denominator principle, since they are the alternative to the other Transport-based processors that require a particular (major) version. Thanks!

[JPercivall]

+1

Visually verified code and did a contrib-check build. In a standalone instance I ran FetchElasticsearchHTTP with and without a "type" hitting a secure 2.3 ES instance. Also used EL for the URL to verify NIFI-3095. Everything worked as expected. Thanks @mattyb149 I will merge it in.