Change projection property in sources options to optional

The `projection` property is not mandatory, the view's projection is used if not provided.

src/ol/source/Image.js

@@ -70,7 +70,7 @@ class ImageSourceEvent extends Event {
 /**
  * @typedef {Object} Options
  * @property {import("./Source.js").AttributionLike} [attributions]
- * @property {import("../proj.js").ProjectionLike} projection
+ * @property {import("../proj.js").ProjectionLike} [projection]
  * @property {Array<number>} [resolutions]
  * @property {import("./State.js").default} [state]
  */