Gracefully handle expired token: prevent `TokenMismatchException`

Please use GitHub reactions 👍 to show that you are affected by the same issue. Please don't comment if you have no relevant information to add!

Is your feature request related to a problem? Please describe.

I just got an error screen with the following info:

App Version: 3.4.19
App Version Code: 3004019
App Flavor: play

Files App Version Code: 30190190

---

OS Version: 4.9.218-perf+(gms-7c69ec7e)
OS API Level: 29
Device: FP3
Manufacturer: Fairphone
Model (and Product): FP3 (FP3)

---

java.lang.RuntimeException: com.nextcloud.android.sso.exceptions.TokenMismatchException: Provided authentication token does not match or package name is not permitted to perform this action
	at io.reactivex.internal.util.ExceptionHelper.wrapOrThrow(ExceptionHelper.java:46)
	at io.reactivex.internal.observers.BlockingMultiObserver.blockingGet(BlockingMultiObserver.java:93)
	at io.reactivex.Maybe.blockingGet(Maybe.java:2321)
	at io.reactivex.Observable.blockingSingle(Observable.java:5381)
	at it.niedermann.owncloud.notes.persistence.NotesServerSyncTask.pullRemoteChanges(NotesServerSyncTask.java:219)
	at it.niedermann.owncloud.notes.persistence.NotesServerSyncTask.run(NotesServerSyncTask.java:96)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:462)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
	at java.lang.Thread.run(Thread.java:919)
Caused by: com.nextcloud.android.sso.exceptions.TokenMismatchException: Provided authentication token does not match or package name is not permitted to perform this action
	at com.nextcloud.android.sso.api.AidlNetworkRequest.performNetworkRequestV2(AidlNetworkRequest.java:188)
	at com.nextcloud.android.sso.api.NextcloudAPI.performNetworkRequestV2(NextcloudAPI.java:199)
	at com.nextcloud.android.sso.api.NextcloudAPI.lambda$performRequestObservableV2$1$com-nextcloud-android-sso-api-NextcloudAPI(NextcloudAPI.java:129)
	at com.nextcloud.android.sso.api.NextcloudAPI$$ExternalSyntheticLambda2.subscribe(Unknown Source:6)
	at io.reactivex.internal.operators.observable.ObservableFromPublisher.subscribeActual(ObservableFromPublisher.java:31)
	at io.reactivex.Observable.subscribe(Observable.java:12284)
	at io.reactivex.internal.operators.observable.ObservableSingleMaybe.subscribeActual(ObservableSingleMaybe.java:31)
	at io.reactivex.Maybe.subscribe(Maybe.java:4290)
	at io.reactivex.Maybe.blockingGet(Maybe.java:2320)
	... 8 more

This happened, I guess, because I had to reinstall the main Nextcloud app.

Describe the solution you'd like

Notice that the token expired and gracefully follow up: inform the user that the token expired and that notes cannot be synced. Offer the option to re-log in, or continue as is for now.

Describe alternatives you've considered

The News app forced me to re-authenticate, which is fine for that app. But for notes it's not great, because it might render my notes temporarily inaccessible (e.g. if I don't have internet access for the moment). So News' approach is not an option.

Additional context

Start with NotesServerSyncTask.java at pullRemoteChanges (line 219) and run (line 96), where the TokenMismatchException appears in the reported stack trace. Trace how sync errors reach the user-facing flow; done means an expired or mismatched token is identified, the user is informed that syncing is unavailable, and re-login or continuing offline is offered.