feat(forwarder): add interfaces to handle a remote terminal session

[rgallor]

Two interfaces has been added to allow managing a remote terminal session:

• io.edgehog.devicemanager.RemoteTerminalRequest: a server-owned interface carrying the configuration data necessary to open a remote terminal from a device to a certain host
• io.edgehog.devicemanager.ForwarderSessionsState: a device-owned interface used by a device to provide information about the status of a remote terminal session (connected / disconnected)

close #62

[harlem88]

I'm not sure but maybe we could add other 2 endpoints for forward_port and protocol_type and call the interface ...DeviceForwarderRequest, so we could use one interface for both RemoteTerminal and DeviceForwarder feature. What do you think?

[harlem88]

Linking the pull request to #62 in the description of PR.

close #62 

[szakhlypa]

Is there any chance we may need to unset session_token with "allow_unset": true?

[rgallor]

From my point of view, the device will either be disconnected (false) or connected (true) in a remote terminal session, so I didn't consider using the allow_unset option.

[szakhlypa]

Do we want to have some error reporting? E.g. when device received RemoteTerminalRequest with hostname it cannot resolve.

[rgallor]

Do we want to have some error reporting? E.g. when device received RemoteTerminalRequest with hostname it cannot resolve.

At the moment only HTTP client errors cause the device to stop attempting to connect with the bridge, but no information is reported (since no interfaces to do so have been defined). @harlem88 @rbino do you think it could be a good idea to introduce this information exchange?

[harlem88]

Do we want to have some error reporting? E.g. when device received RemoteTerminalRequest with hostname it cannot resolve.

At the moment only HTTP client errors cause the device to stop attempting to connect with the bridge, but no information is reported (since no interfaces to do so have been defined). @harlem88 @rbino do you think it could be a good idea to introduce this information exchange?

I think it is a good idea but for the first forwarder implementation we will keep it basic, so we will introduce the error reporting later.