NIFI-5909 PutElasticsearchHttpRecord doesn't allow to customize the timestamp format

[SavtechSolutions]

added optional settings for date, time, and timestamp formats used to write Records to Elasticsearch

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[SavtechSolutions]

No unit tests have been added/modified, as existing tests verify only the URL used to call ES, but not the content. I'm thinking of adding a callback hook to the realRequest inside PutElasticsearchHttpRecordTestProcessor.createElasticsearchClient() to do any custom content assertions

Never mind this, added the tests already

[patricker]

I'm not a good reviewer for this one, but anything you can do to add test cases and improve the overall quality is appreciated, and makes it easier for current and future code changes/reviews.

[SavtechSolutions]

Yes, I do plan to add them - time permitting, as there's some infrastructure coding I need to do first, to make content assertions possible.

[bdesert]

@SavtechSolutions ,
IMO, descriptions for time/date/timestamp descriptors should be consistent with existing ones. Please take a look at CSVReader for example.
Also, having expression language allowed on flow file level can cause inconsistency of date/time/timestamp data fields in ES. I would restrict it to Variable Registry level.

Also, before you commit the changes, you could run
mvn -T 2 clean install -Pcontrib-check -Ddir-only
to make sure you don't have styling issues and all tests are passing.

[bdesert]

+1 LGTM. Pulled the changes and rebuilt the instance. Tested with different formats. Thank you for improvements! Merging to master.