http: replace WorkQueue and single threads handling for ThreadPool #273
Description
mentioned in: bitcoin#33689
"You know, we could call ProcessTask() during Stop() too, which would be a strict improvement over the current locking-wait behavior in master (since we would shut down faster by actively processing pending requests on the shutdown thread as well). This is something that hasn’t been possible until now.
Still, this is material for a follow-up; would say that it is better to keep this PR as contained as possible so all other PRs and working paths that depend on this structure can actually make use of it." - furszy