feat(agents): Add Deezer API artist image provider agent (#4180)

* feat(agents): Add Deezer API artist image provider agent

* fix(agents): Use proper naming convention of consts

* fix(agents): Check if json test data can be read

* fix(agents): Use underscores for unused function arguments

* fix(agents): Move int literal to deezerArtistSearchLimit const

* feat: add Deezer configuration option to disable it.

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>
Co-authored-by: Deluan Quintão <deluan@navidrome.org>

core/agents/deezer/responses.go

@@ -0,0 +1,31 @@
+package deezer
+
+type SearchArtistResults struct {
+	Data  []Artist `json:"data"`
+	Total int      `json:"total"`
+	Next  string   `json:"next"`
+}
+
+type Artist struct {
+	ID            int    `json:"id"`
+	Name          string `json:"name"`
+	Link          string `json:"link"`
+	Picture       string `json:"picture"`
+	PictureSmall  string `json:"picture_small"`
+	PictureMedium string `json:"picture_medium"`
+	PictureBig    string `json:"picture_big"`
+	PictureXl     string `json:"picture_xl"`
+	NbAlbum       int    `json:"nb_album"`
+	NbFan         int    `json:"nb_fan"`
+	Radio         bool   `json:"radio"`
+	Tracklist     string `json:"tracklist"`
+	Type          string `json:"type"`
+}
+
+type Error struct {
+	Error struct {
+		Type    string `json:"type"`
+		Message string `json:"message"`
+		Code    int    `json:"code"`
+	} `json:"error"`
+}