MINOR: cli/applet: Move appctx fields only used by the CLI in a private context

MINOR: cli/applet: Move appctx fields only used by the CLI in a private context

There are several fields in the appctx structure only used by the CLI. To
make things cleaner, all these fields are now placed in a dedicated context
inside the appctx structure. The final goal is to move it in the service
context and add an API for cli commands to get a command coontext inside the
cli context.