Enable filtering rack reservations by user

[jeremystretch]

Environment

• Python version: 3.6.9
• NetBox version: 2.10.1

Proposed Functionality

Add a widget to the rack reservations list to allow filtering by assigned user. (The filtering logic to support this is already in place; just need to add the form field.)

Use Case

Allow convenient filtering of rack reservations by assigned user.

Database Changes

None

External Dependencies

None