default start all services, but accept config

[b5]

this PR changes the default for iroh start back to {gateway,store,p2p}, but now iroh CLI reads a new cli.config.toml file that accepts a single configuration parameter. We can use this to get back the "only gateway & store" behaviour with an installer script that makes cli.config.toml.

# when running on a laptop, only turn on the gateway & store by default
start_default_services = [
  "gateway",
  "store",
]

I've kept iroh start --all, because it's still useful to have a CLI flag that overrides what's started in any case

[Arqu]

Code LGTM. Tested locally, works like a charm.