Add mode=... for data.frame ingestion

[eddelbuettel]

This PR follows the lead ot the Python package and adds a mode argument for array creation from data.frame objects. A unit tests ensures the behaviour of ingest (schema + write), schema_only and append are as expected.

[shortcut-integration]

This pull request has been linked to Shortcut Story #13938: Support ingest, schema_only, append modes for data.frame ingestion..

[aaronwolen]

Looks great. Thanks, @eddelbuettel!

[eddelbuettel]

How about also adding this to the new vignette?

modified   vignettes/data-ingestion-from-sql.md
@@ -105,6 +105,10 @@ storeDataTDB <- function(dat, uri) {
 }

+The mode="append" argument of fromDataFrame can be used to append to an existing array to
+support chunked operation.
+
+

Reading Data Back In

Reading data from TileDB is a very standard operation of opening the URI, possibly specifying the