Check for projector getting doc values that are too big

For any document, the 20 MB limit applies to document body + User xattrs.
Memcached reserves a buffer of 1 MB for System xattrs.
While streaming a document to a DCP consumer, KV will stream body + user xattrs + system xattrs.
Hence, consider a case where the document body is 19.9 MB. With 1 MB of system xattr buffer fully used, KV will sent 19.9 + 1 = 20.9 MB to the consumer.

This gives a projector error and goes into a loop of error.

Linked to MB-38269