Use repr for error logging

[Ruwann]

Follow-up on #1708 (comment)

As mentioned there, there is a __repr__ but not a __str__, leading to an empty log message (for HTTPExceptions).

An example when running the dev server (previously the first line would just be an empty line):

HTTPException(status_code=404, detail='Not Found')
INFO:     127.0.0.1:33538 - "GET /swaggers/ui/ HTTP/1.1" 404 Not Found

However, I would also be fine with just removing the logging here as HTTPExceptions can be part of the normal flow, without indicating an actual application error (case in point: raising a Not Found exception)

[coveralls]

coverage: 94.045%. remained the same when pulling c30f74b on Ruwann:bugfix/exception-log into 55f3c59 on spec-first:main.

[RobbeSneyders]

Thanks @Ruwann!

I think it's fine to log just the error when a handler is registered, and a traceback when no handler is available.