BulkInsert/BulkInsertAsync with IEnumerable / IAsyncEnumerable

[e-tobi]

BulkInsert() currently consumes a IReadOnlyCollection. I think, it would be nice to allow IEnumerable too and even IAsyncEnumerable. This would allow to "stream" a large amount of documents into the database. I can provide a PR for this, if this is something that might get accepted

BTW: BulkInsertDocuments()/BulkInsertDocumentsAsync() already takes an IEnumerable, but I think this is misleading, because the documents will be grouped by type, causing the whole enumerable to be enumerated and loaded into memory. Having a potentially large data source, which provides an IEnumerable via yielding, this may cause trouble.