Allow interfaces list to be filtered on mgmt_only

[candlerb]

Environment

• Python version: 3.6.9
• NetBox version: 2.10.2

Proposed Functionality

In the interfaces list /dcim/interfaces/ (#3564), add the ability to filter on the mgmt_only flag (#5569).

Currently it's possible to view this as a column (go to Configure cog, add "OOB Management"), but not to filter on it.

Use Case

General usefulness - "do I have any OOB interfaces in site X? If so, what are they?"

Database Changes

None

External Dependencies

None. Presumably the implementation would be the same as filtering on the "Enabled" flag, which already exists.