Add artistImageUrl available in getArtists endpoint

Also cache artist info in the DB for 1 hour

db/migration/20201030162009_add_artist_info_table.go

@@ -0,0 +1,35 @@
+package migration
+
+import (
+	"database/sql"
+
+	"github.com/pressly/goose"
+)
+
+func init() {
+	goose.AddMigration(upAddArtistImageUrl, downAddArtistImageUrl)
+}
+
+func upAddArtistImageUrl(tx *sql.Tx) error {
+	_, err := tx.Exec(`
+alter table artist
+	add biography varchar(255) default '' not null;
+alter table artist
+	add small_image_url varchar(255) default '' not null;
+alter table artist
+	add medium_image_url varchar(255) default '' not null;
+alter table artist
+	add large_image_url varchar(255) default '' not null;
+alter table artist
+	add similar_artists varchar(255) default '' not null;
+alter table artist
+	add external_url varchar(255) default '' not null;
+alter table artist
+	add external_info_updated_at datetime;
+`)
+	return err
+}
+
+func downAddArtistImageUrl(tx *sql.Tx) error {
+	return nil
+}