Http errors below 500 shouldn't log errors.

**Is your feature request related to a problem? Please describe.**

We're currently getting many error logs in our service just because a user might pass in the wrong collection name. I see that `API` indiscriminately logs everything it receives in `get_exception` as an error: https://github.com/geopython/pygeoapi/blob/master/pygeoapi/api/__init__.py#L578.

**Describe the solution you'd like**

Errors below 500 should not be logged as errors. It produces noise and causes external logging services to send many false positives. Such errors can be logged as a warning or info, and a proper message should be returned to the client.

I can make a change for this if the idea is acceptable.

**Describe alternatives you've considered**

**Additional context**