Allow IndexCoordinates in repositories

[ls-urs-keller]

It is common to have multiple indexes with the same document structure. E.g. rolling indices over time and having a wildcard alias. Sometimes one wants to select different IndexCoordinates than specified in @Document(indexName = "...", ...). Also you might want to use the same Repository to do cross cluster searches and for this need to specify the IndexCoordinates.

It would therefore be helpful to support IndexCoordinates as an argument to repository methods the same way ScrollPosition, Sort and Pageable are handled.

This PR is an attempt to introduce this change. I keep it as draft to get some comments I can add tests to it if we can agree on the change being valid.

[sothawo]

I'll have a look at this later that week or probably on the weekend, I'm on a business trip currently and won't find the time earlier