Wallet has no warning for stale balance

[SWvheerden]

The wallet returns stale balance results with no warning to the user if it cannot
get a live state from the base node. This will lead clients to use stale results.
There is no way to distinguish between stale and updated results.
This is because the GetBalance operation uses the get_chain_metadata function to
calculate the current tip. GetChainMetadata in turn will return an Ok result even
when it fetches possibly outdated data from its database.

            OutputManagerRequest::GetBalance => {
                let current_tip_for_time_lock_calculation = match 
self.base_node_service.get_chain_metadata().await {
                    Ok(metadata) => metadata.map(|m| 
m.height_of_longest_chain()),
                    Err(_) => None,
                };
                self.get_balance(current_tip_for_time_lock_calculation)
                    .map(OutputManagerResponse::Balance)
            },
            BaseNodeServiceRequest::GetChainMetadata => match 
self.get_state().await.chain_metadata {
                Some(metadata) => 
Ok(BaseNodeServiceResponse::ChainMetadata(Some(metadata))),
                None => {
                    // if we don't have live state, check if we've 
previously stored state in the wallet db
                    let metadata = self.db.get_chain_metadata()?;
                    
Ok(BaseNodeServiceResponse::ChainMetadata(metadata))
                },
            },

Provide a clear warning to users that they are getting outdated data