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>

core/agents/local_agent.go

@@ -21,7 +21,7 @@ func (p *localAgent) AgentName() string {
 	return LocalAgentName
 }
 
-func (p *localAgent) GetTopSongs(ctx context.Context, id, artistName, mbid string, count int) ([]Song, error) {
+func (p *localAgent) GetArtistTopSongs(ctx context.Context, id, artistName, mbid string, count int) ([]Song, error) {
 	top, err := p.ds.MediaFile(ctx).GetAll(model.QueryOptions{
 		Sort:  "playCount",
 		Order: "desc",