Simplify starting how we start local Jupyter, remote Jupyter and raw kernels (part 2)

[DonJayamanne]

Part of #12832, #12831

Before (steps to start a kernel)

IJupyterNotebookProvider.connect(): connection
IJupyterNotebookProvider.createNotebook()               
   IJupyterServerProvider.getOrCreateServer()   
       IJupyterExecution.getServer()  
           ServerCache.getOrCreate(): INotebookServer
   INotebookServer.createNotebook()
       JupyterSessionManager.startNew(): Session

After (we now have clear and distinct classes with specific responsibilities)

IJupyterNotebookProvider.startJupyter(): connection
IJupyterSessionManagerFactory.create(connection): SessionManager 
JupyterSessionManager.startNew(): Session