Add a default host and port for the microgrid client

[leandro-lucarella-frequenz]

What's needed?

A default host and port to connect to when connecting to the microgrid API.

Proposed solution

The SDK used to provide a default host and port to connect to:

DEFAULT_NITROGEN_HOST = "[::1]"
DEFAULT_NITROGEN_PORT = 61060

We could also provide a default host and port but the MicrogridGrpcClient takes a grpc.aio.Channel directly, so all the connections parameters should be set outside of the client.

We could provide just bare constants that the user could use when creating the channel, but the usefulness of that might be reduced.

Another option would be to add constructors to create the GRPC channel in the client, but then the client should decide on other parameters of the channel, like if it is secure or insecure, for which it should probably need to take extra parameters, also limiting its usefulness.

Use cases

No response

Alternatives and workarounds

No response

Additional context

No response