Summarise runtime config at startup

[itowlson]

Via @mikkelhegn, broken out from #1850:

I still think at least an acknowledgement of what runtime config was loaded would be great. ...

Using [llm_remote] and [key_value_store.remore_redis] runtime-config from /mikkels/fancy/setup.toml

That level of detail I think would be a good balance.

(Ivan again) Printing the file name is particular attractive if the runtime config is coming from an environment variable where it's not visible on the command line.