Refresh folder when app is active

[tobiasKaminsky]

• Android feat(file-list): folder refresh scheduler android#16646

• iOS

• when user is in app and in a folder list

• refresh every 30s (first via cheap eTag call)

• make sure to stay at same position in list after refresh (not scroll up to top)

This way the user always has an up to date view

[alperozturk96]

Android PR: nextcloud/android#16646