Store the first provider even if no distributor is available, else error in troubleshoot test will not be accurate.

Also when registering for the first time, pick the fist available provider with at least one distributor.

libraries/push/api/src/main/kotlin/io/element/android/libraries/push/api/PushService.kt

@@ -44,6 +44,15 @@ interface PushService {
         distributor: Distributor,
     ): Result<Unit>
 
+    /**
+     * Store the given push provider as the current one, but do not register.
+     * To be used when there is no distributor available.
+     */
+    suspend fun selectPushProvider(
+        matrixClient: MatrixClient,
+        pushProvider: PushProvider,
+    )
+
     fun ignoreRegistrationError(sessionId: SessionId): Flow<Boolean>
     suspend fun setIgnoreRegistrationError(sessionId: SessionId, ignore: Boolean)