Import from folder notification source

[tlourey]

Environment

• Nautobot version: 2.1.0
• nautobot-circuit-maintenance version: v0. 6.2

Proposed Functionality

Create additional notification source of folder import.

Use Case

If you had a postfix server or some other system that put email messages in a folder somewhere, regularly checking that folder for new files then processing them as notification emails would be useful if you didn't want to use Gmail or Google workspace or imaps