Internal: add indices setter to IndicesRequest interface

We currently expose generic getters for indices and indicesOptions on the IndicesRequest interface. This commit adds a generic setter as well, which can be used to set the indices to a request. The setter impl throws `UnsupportedOperationException` if called on internal requests. Also throws exception if called on single index operations, since it accepts an array as argument.
review round: introduced IndicesRequest.Replaceable interface