Add outgoing packet type "kdeconnect.share.request.update" to allow android to update the share notification

Summary

Add outgoing packet type "kdeconnect.share.request.update" that is used to notify the remote device that additional files have been added to the currently running share request.

Test Plan

Apply both this patch and the companion kdeconnect-android patch Share a big file from desktop to android While the big file is being uploaded share 1 or more additional files with the same android device and observe that the notification on android is updated to reflect the new situation (eg. "Receiving x files from xxx" and "(File x of x): xxxx" is being displayed)