`ping` style health check method to return a valid connection to the command centre

**Is your feature request related to a problem? Please describe.**
While implementing a user interface we wanted to display a connectivity status to the Command Centre.

I necessarily don't want to fetch any data from the Command Centre, but just want to know that the credentials are valid and that the client can speak with the Command Centre.

I assumed that there's network connectivity (although the client should fail if there is no network).

At the moment I can check to see if the version number constant or the `good_known_version` is set, but that should really be an internal construct and should not be used be the external API users.

**Describe the solution you'd like**
Expose a `ping` or `alive` style method that returns a positive response when:
- There's network connectivity
- Command Centre is reachable via the Cloud or Direct connection (depending on how the client is initialised)
- API key and Certificate configuration is valid
- Discover #5 has worked and the API client is ready to communicate to the CC

```python
cc.ping() == True
```

**Describe alternatives you've considered**
NA

**Additional context**
NA