Notify users when the graph is not in sync

[llunaCreixent]

And maybe try to rely in the graph as little as possible.

[triaslucia]

@llunaCreixent This is important for new Notification System we are currently designing.

1_Could you write in here as short as possible what the actual error is? 2_Also could you tell me if there is any push-up notification at the moment related to this error?

[louilinn]

This has low priority as we haven't had problems with The Graph for a long time, after switching to self hosted subgraph