Automation client: add an API to get a session using a token

We need to be able to make automation calls using the token based authentication plugin done in NXP-10268.
The principle is to add an API to the AutomationClient to allow getting a client Session following these steps:

• First acquire a token remotely from the server (thanks to the token authentication plugin for example) using parameters gathered by the client.
• Store this token locally for later use.
• Use the token to get a Session passing it as a request header, readable by the token authentication plugin.

A TokenCallback interface will define the API to gather the token parameters, acquire a remote token, save it locally, read it locally.