feat(playlists): optional start rank for play_playlist

proto/player.proto

@@ -78,4 +78,5 @@ message TracksRequest {
 
 message PlayPlaylistRequest {
 	uint32 id = 1;
+	optional uint32 starting_rank = 2;
 }

src/player.rs

@@ -259,8 +259,11 @@ impl Player for PlayerService {
 
         let tracks = playlist.tracks.iter().map(|t| t.clone().into());
 
-        let tracks_and_paths: Vec<(Track, PathBuf)> =
-            tracks.into_iter().zip(track_paths.into_iter()).collect();
+        let tracks_and_paths: Vec<(Track, PathBuf)> = tracks
+            .into_iter()
+            .zip(track_paths.into_iter())
+            .skip(input.starting_rank.unwrap_or(0) as usize)
+            .collect();
 
         if let Err(_) = player.add_tracks_to_queue(tracks_and_paths, true).await {
             return Err(tonic::Status::internal(""));