adds get_user_profile()

[DerKO9]

This adds the get_user_profile() that can be found in the other librespot implementations, such as:
Rust (https://github.com/librespot-org/librespot/blob/33bf3a77ed4b549df67e8347d7d6e55b007b3ec2/core/src/spclient.rs#L675)
or
Java (https://github.com/librespot-org/librespot-java/blob/52a8c24215e5a9b921da8e7219c49937ec87ed88/lib/src/main/java/xyz/gianlu/librespot/dealer/ApiClient.java#L254)

This tries to write the same function in python. The response is a JSON object instead of a protobuf response and looks something like this:

{
  "uri": "spotify:user:[USER_ID]",
  "name": "[USER_DISPLAY_NAME]",
  "public_playlists": [
    {
      "uri": "spotify:playlist:[PLAYLIST_ID]",
      "name": "test",
      "image_url": "spotify:image:ab67616d00001e0208fdcdc2c63b05d8be1b7d61",
      "followers_count": 1,
      "owner_name": "[USER_DISPLAY_NAME]",
      "owner_uri": "spotify:user:[USER_ID]",
      "is_following": true
    },
    {
      "uri": "spotify:playlist:[PLAYLIST_ID]",
      "name": "test2",
      "image_url": "spotify:image:ab67616d00001e0232f1572738340ddc9569c54b",
      "owner_name": "[USER_DISPLAY_NAME]",
      "owner_uri": "spotify:user:[USER_ID]",
      "is_following": true
    },
    {
      "uri": "spotify:playlist:[PLAYLIST_ID]",
      "name": "test3",
      "image_url": "spotify:mosaic:ab67616d00001e024803dc88ae15cc228778477a:ab67616d00001e024ac2d979712c58dcc49290e0:ab67616d00001e0290c9072fbd484299e0f624ca:ab67616d00001e02bbf6867de49bfcc7c7dd8229",
      "owner_name": "[USER_DISPLAY_NAME]",
      "owner_uri": "spotify:user:[USER_ID]",
      "is_following": true
    }
  ],
  "total_public_playlists_count": 5,
  "is_current_user": true,
  "has_spotify_name": true,
  "color": 11836360,
  "allow_follows": true,
  "show_follows": true
}