Get album info (when available) from Last.fm, add getAlbumInfo endpoint (#2061)

* lastfm album.getInfo, getAlbuminfo(2) endpoints

* ... for description and reduce not found log level

* address first comments

* return all images

* Update migration timestamp

* Handle a few edge cases

* Add CoverArtPriority option to retrieve albumart from external sources

* Make agents methods more descriptive

* Use Last.fm name consistently

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

conf/configuration.go

@@ -243,7 +243,7 @@ func init() {
 	viper.SetDefault("ignoredarticles", "The El La Los Las Le Les Os As O A")
 	viper.SetDefault("indexgroups", "A B C D E F G H I J K L M N O P Q R S T U V W X-Z(XYZ) [Unknown]([)")
 	viper.SetDefault("probecommand", "ffmpeg %s -f ffmetadata")
-	viper.SetDefault("coverartpriority", "embedded, cover.*, folder.*, front.*")
+	viper.SetDefault("coverartpriority", "cover.*, folder.*, front.*, embedded, external")
 	viper.SetDefault("coverjpegquality", 75)
 	viper.SetDefault("uiwelcomemessage", "")
 	viper.SetDefault("enablegravatar", false)