expose partial matches

[philsippl]

Extends the UniquenessResult with partial results for both eyes.

pub struct UniquenessResult {
    // ...
    pub matched_serial_ids:       Option<Vec<u32>>,
    pub matched_serial_ids_left:  Option<Vec<u32>>, // New
    pub matched_serial_ids_right: Option<Vec<u32>>, // New
}

[philsippl]

consumer of this message (signup service) probably need to get adapted to additional fields, please do before merging.