Add initial data from request.GET to script forms

[steffann]

Environment

• Python version: 3.6.7
• NetBox version: 2.6.11

Proposed Functionality

Most NetBox forms are passed initial=request.GET to the constructor so that the request can pass initial values to the form. The extra/scrips functionality doesn't do that. I propose to add it to make forms behaviour consistent.

Use Case

I have a script that requires the user to select a device. With initial=request.GET I would be able to create a custom link from the device page with URL /extras/scripts/example/demo/?router={{ obj.id }} so that a user can easily click from the device page to the script page with the correct device pre-selected.

Database Changes

None

External Dependencies

None

As usual I'll implement this myself once accepted.