Add note to docs regarding multi-get ordering
Add note to docs regarding multi-get ordering

The implementation maintains the order of the original requests yet this
functionality is not documented. This commit adds a note to the docs
regarding the ordering of responses to an multi-get request.

Relates #28356

strapdata/elassandra,strapdata/elassandra,strapdata/elassandra,strapdata/elassandra,vroyer/elassandra,vroyer/elassandra,vroyer/elassandra,strapdata/elassandra