Fix submit button in crop by adding id (#2374)

- Add missing ID to submit button in crop page.

src/main/resources/templates/crop.html

@@ -22,7 +22,7 @@
                 <input id="y" type="hidden" name="y">
                 <input id="width" type="hidden" name="width">
                 <input id="height" type="hidden" name="height">
-                <button type="submit" class="btn btn-primary" th:text="#{crop.submit}"></button>
+                <button id="submitBtn" type="submit" class="btn btn-primary" th:text="#{crop.submit}"></button>
               </form>
               <div id="canvasesContainer" style="position: relative; margin: 20px 0; width: auto;">
                 <canvas id="cropPdfCanvas" style="width: 100%"></canvas>