feat(server): Fetch icon url of an instance (#6591)

* feat(server): Fetch icon url of an instance

Resolve #6589

* chore: Rename the function

src/models/entities/instance.ts

@@ -158,6 +158,11 @@ export class Instance {
 	})
 	public maintainerEmail: string | null;
 
+	@Column('varchar', {
+		length: 256, nullable: true, default: null,
+	})
+	public iconUrl: string | null;
+
 	@Column('timestamp with time zone', {
 		nullable: true,
 	})