Agent YAML Tool should allow limiting to a sub-set of a server's tools

[vorburger]

https://docs.enola.dev/concepts/tool should allow limiting an agent to a subset of tools from a server.

E.g. for #1882 with https://github.com/nspady/google-calendar-mcp#available-tools, it should be possible to use:

tools:
- google-calendar#get-freebusy