Allow resolveEntry to be overriden on select2. Override it on nuxeo-user-suggestion

The nuxeo-user-suggestion has a "prefixed" mode , in which the "prefixed_id" is used instead of "id" field.

-select2-behaviour uses has a "resolveEntry" function that "transforms" input entries into objects with "id" and "displayLabel" fields.

-when using the nuxeo-user-suggestion in the "prefixed" mode, these two fields are not be enough as it requires a "prefixed_id" field that is not there.

Therefore, the resolveEntry must be allowed to be overriden and the nuxeo-user-suggestion should override it.