This commit removes the search preference _only_node as the same
functionality can be obtained by using the search preference
_only_nodes. This commit also adds a test that ensures that _only_nodes
will continue to support specifying node IDs.
Relates #18875
The search preference _prefer_node allows specifying a single node to
prefer when routing a request. This functionality can be enhanced by
permitting multiple nodes to be preferred. This commit replaces the
search preference _prefer_node with the search preference _prefer_nodes
which supplants the former by specifying a single node and otherwise
adds functionality.
Relates #18872
Just like specifying `?preference=_primary`, this adds the ability to
specify `?preference=_replica` or `?preference=_replica_first` on
requests that support it.
Resolves#12222
Jason Tedor
Isabel Drost-Fromm
Lee Hinman
Nirmal Chidambaram
Clinton Gormley