Request to Add addLabeledDescriptors Method and Support for Empty FaceMatcher Initialization

[Rann-Studio]

Currently, FaceMatcher requires an initial set of labeled descriptors when it is created. However, it would be more flexible if we could create an empty FaceMatcher instance (without any labeled descriptors) and later add labeled descriptors dynamically using a method like addLabeledDescriptors.

I propose the following two changes:

1. Support for Empty Initialization: Allow new faceapi.FaceMatcher() to be called without any initial labeled descriptors. This would enable users to instantiate a FaceMatcher without needing to provide labels upfront.

2. addLabeledDescriptors Method: Add a method that allows new labeled descriptors to be appended to an existing FaceMatcher instance after it has been initialized, enabling the dynamic addition of labels.

// Create an empty FaceMatcher instance
const faceMatcher = new faceapi.FaceMatcher();

// Add labeled descriptors dynamically
faceMatcher.addLabeledDescriptors('newPerson', newFaceDescriptor);