Exclude /metrics from LOGIN_REQUIRED regression

[craized]

NetBox version

v3.1.0

Python version

3.7

Steps to Reproduce

Set LOGIN_REQUIRED = True
Query /metrics endpoint

Expected Behavior

Receive metrics dump

Observed Behavior

Redirect to login page

Confirmed disabling LOGIN_REQUIRED allows fetching of /metrics
Reference issue for previous versions: #3123

[jeremystretch]

Seems that the URL provided by django_prometheus does not include a trailing slash.

[craized]

TYVM! Patch speed is second-to-none