Expose the overload descriptors lines

This MR solves relay-search#40005 (closed) exposing he overload-general descriptor line via the details document to be added to relay search. Operators that use relay-search to check their relays will find information on how to get the metricsport details into prometheus for their own analysis (see: library#40008 (comment 2746714)).

It also exposes the overload-ratelimits and overload-fd-exhausted lines in the bandwidth document. These are meant to be used by the network healh tooling and not yet by relay-search. Operators that query onionoo will also be able to use this information.

Depends on: library!5 (merged)