Adds event to signal teosd is ready

[sr-gi]

This adds an event to teosd that can be used to check when it has finished bootstrapping. This is specially useful when testing, since otherwise arbitrary waits have to be added to avoid querying non initialised services.

Summary:

• Adds a multiprocess event to the RPC server that gets set once it is ready
• Adds a ping endpoint to the API that gets polled to check if the API is ready
• Adds an event to teosd that gets set when the two previous events get set

close #214