[ANR] Key backup realm transaction on main thread

```
at io.realm.BaseRealm.beginTransaction (BaseRealm.java:2)
at io.realm.Realm.executeTransaction (Realm.java:8)
at org.matrix.android.sdk.internal.crypto.store.db.HelperKt.doRealmTransaction (Helper.kt:2)
at org.matrix.android.sdk.internal.crypto.store.db.RealmCryptoStore.setKeysBackupData (RealmCryptoStore.kt:1)
at org.matrix.android.sdk.internal.crypto.keysbackup.DefaultKeysBackupService.access$enableKeysBackup (DefaultKeysBackupService.kt:13)
at org.matrix.android.sdk.internal.crypto.keysbackup.DefaultKeysBackupService$checkAndStartWithKeysBackupVersion$1.onSuccess (DefaultKeysBackupService.kt:17)
at io.reactivex.internal.util.Pow2.foldToCallback (Pow2.java:2)
at org.matrix.android.sdk.internal.task.TaskExecutor$execute$1.invokeSuspend (TaskExecutor.kt:14)
at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith (ContinuationImpl.kt:3)
at kotlinx.coroutines.DispatchedTask.run (DispatchedTask.kt:18)
at android.os.Handler.handleCallback (Handler.java:938)
at android.os.Handler.dispatchMessage (Handler.java:99)
at android.os.Looper.loop (Looper.java:246)
at android.app.ActivityThread.main (ActivityThread.java:8595)
```