gui: Disable Cleanup Interval with External File Versioning as unsupported (#7360)

As for right now, the External File Versioning does not support Cleanup
Interval. Therefore, the option should no be available at all when using
it.

Ref: https://forum.syncthing.net/t/16346

Signed-off-by: Tomasz Wilczyński <[email protected]>

gui/default/syncthing/folder/editFolderModalView.html

@@ -146,7 +146,7 @@
               <span translate ng-if="folderEditor.externalCommand.$error.required && folderEditor.externalCommand.$dirty">The path cannot be blank.</span>
             </p>
           </div>
-          <div class="form-group" ng-if="currentFolder._guiVersioning.selector != 'none'" ng-class="{'has-error': folderEditor._guiVersioning.cleanupIntervalS.$invalid && folderEditor._guiVersioning.cleanupIntervalS.$dirty}">
+          <div class="form-group" ng-if="currentFolder._guiVersioning.selector != 'none' && currentFolder._guiVersioning.selector != 'external'" ng-class="{'has-error': folderEditor._guiVersioning.cleanupIntervalS.$invalid && folderEditor._guiVersioning.cleanupIntervalS.$dirty}">
             <label translate for="versioningCleanupIntervalS">Cleanup Interval</label>
             <div class="input-group">
               <input name="versioningCleanupIntervalS" id="versioningCleanupIntervalS" class="form-control text-right" type="number" ng-model="currentFolder._guiVersioning.cleanupIntervalS" required="" min="0" max="31536000" aria-required="true" />