When changing SD Card user should get a migration option

[childnode]

Actual behaviour

• change the SD Card (incl. Backup)
• all uploads / downloads fails without giving a hint about the cause

Expected behaviour

• When Changing an SD Card and storage path gets outdated / inaccessible, guide the user by saying "Storage Folder is not accessible" to the setting to allow him to move over to a new path
• pause downloads / uploads unless a valid path is set to avoid error notifications

possibly:

• auto-detect a changed SD Card an just ask if we should temporarily ignore this - means pause nextcloud - or if we should notice the swap

PLUS:

• When storage path set is no longer available in selection for new users, give a hint to let user set a new (secure) path (incl. migration << issue Nextcloud android app does not move or delete original files #1048)

Steps to reproduce

1. existing installation with external external SD Card set as storage path:
   /storage/0381-09EC/Android/data/com.nextcloud.client/files (aside that this is too technical "Storage path" setting is too technical #1088) it is now outdated?! (referring to Nextcloud android app does not move or delete original files #1048) << no Kitakat+ SD Card formatted as internal Storage extension!
2. change the SD Card (possibly user story: change to use a bigger one)
3. uploads / downloads fail
4. you have to manually find the cause and setting yourself,

Actually it is even not possible for technical advised users to just select the new SD Card which has a 1:1 copy of the old
due to the fact, that there are now paths in the selection, that doesn't allow to reuse the copied data on the SD Card (referring to path mentioned in step 1)
** /storage/emulated/0/Android/media/com.nextcloud.client aka internal Storage
** /storage/B840-C408/Android/media/com.nextcloud.client aka external Storage / new SD Card
** /data/user/0/com.nextcloud.client/files ?!? whatever
** /data/emulated/0/Android/data/com.nextcloud.client/files (internal again, but path different to option 1 but would match what was set on my previous SD Card)

^ user: lost

Environment data

Android version: 7.1.1

Device model: Moto G 4 Play

Stock or customized system: Stock

Nextcloud app version: 3.2.0 (actually latest)