Associates metadata with component describing what values
the component provides for others to use. Provides are specified
as a map keys. Keys in the map correspond to key in context map.
Values in the map are they keys in the component where provieded
value is. The value can be a IFn so if you need to retrieve
nested value you can use e.g. `(comp :foo :bar)`.
Alternatively, if the keys are the same in both the component and
context, they map be specified as vector of keys.