NetBox DNS is incompatible with NetBox < 3.5.8

[peteeckel]

Versions
NetBox Version: 3.5.0 - 3.5.7
NetBox DNS Version: 0.20.2
Python Version: 3.8+

Describe the bug
NetBox DNS is incompatible with NetBox 3.5.0-3.5.7. When the plugin is loaded, these NetBox versions fail to start up, raising an ImportError exception.

To Reproduce
Steps to reproduce the behavior:

1. Install one of the older NetBox 3.5 releases
2. Install and configure NetBox DNS 0.20.2

Expected result
NetBox can be started and NetBox DNS is active

Actual result
NetBox fails to start and an ImportError exception is raised. See #90.

The issue is caused by a code change in NetBox 3.5.8 that broke the import for the get_plugin_config method. This was fixed by the core team in NetBox 3.5.9, but now there are two different import statements depending on whether NetBox 3.5.8 or any other supported release is used. This makes NetBox DNS require at least NetBox version 3.5.8, which is an unnecessary restriction.