Divide candidate faces into groups based on face similarity.<br />

• The output is one or more disjointed face groups and a messyGroup. A face group contains faces that have similar looking, often of the same person. Face groups are ranked by group size, i.e. number of faces. Notice that faces belonging to a same person might be split into several groups in the result.
• MessyGroup is a special face group containing faces that cannot find any similar counterpart face from original faces. The messyGroup will not appear in the result if all faces found their counterparts.
• Group API needs at least 2 candidate faces and 1000 at most. We suggest to try Face - Verify when you only have 2 candidate faces.
• The 'recognitionModel' associated with the query faces' faceIds should be the same.