Collection responses should support `numberMatched` and `numberReturned`

[jkeifer]

Any endpoints returning a collection of objects should support the inclusion of numberMatched and numberReturned. These should not be required parameters where implementation is unknown (user-provided implementations), but should be optional and encouraged wherever possible to provide. See the OGC Features API response object for more information on the basis for these properties.

#123 is an example of adding support for numberMatched to the order collection response.

[jkeifer]

Added a corresponding issue on the spec side: stapi-spec/stapi-spec#300.