JWT logging improvements (#5823)

* lower level on auth success from info to debug (fixes #5820)
* don't log stacktraces on auth errors (as requested on slack). we do this by introducing an `AuthError` type instead of using `anyhow` and `bail`.
* return errors that have been censored for improved security.

pageserver/src/http/routes.rs

@@ -1671,6 +1671,8 @@ where
         );
 
         match handle.await {
+            // TODO: never actually return Err from here, always Ok(...) so that we can log
+            // spanned errors. Call api_error_handler instead and return appropriate Body.
             Ok(result) => result,
             Err(e) => {
                 // The handler task panicked. We have a global panic handler that logs the