Should clean up TSHttpTxnConfigFind #4211
Description
While setting up a PR that removes a overridable config, I ran across TSHttpTxnConfigFind which implements a mapping from configuration string name to enum and type. Rather than implementing this as a map initialized from the existing list of overridable types, it is a nested case statement. Which seems very fragile. The comment at the top of the function says it is suboptimal and should not be used on the fast path. So at that point, we might as well make it maintainable and hard to break.