OutboundLanesCongestedSignals: StorageDescriptor<[Key: FixedSizeBinary<4>], boolean, false, never>

Map of lane id => is congested signal sent. It is managed by the bridge_runtime_common::LocalXcmQueueManager.

bridges-v1: this map is a temporary hack and will be dropped in the v2. We can emulate a storage map using sp_io::unhashed storage functions, but then benchmarks are not accounting its proof_size, so it is missing from the final weights. So we need to make it a map inside some pallet. We could use a simply value instead of map here, because in v1 we'll only have a single lane. But in the case of adding another lane before v2, it'll be easier to deal with the isolated storage map instead.