Allow Change of Default For Config-Context YAML JSON toggle mode

[a31amit]

Environment

• Python version: 3.6
• NetBox version: 2.7 latest

Proposed Functionality

Please allow a Configuration option for Default Setting Config-Context YAML JSON toggle mode.

Use Case

This will help netbox admins and users to set the preferred mode for their userbase

Database Changes

None

External Dependencies

None

[DanSheps]

Similar to #1426 and would be blocked by #3294, I can get behind this however, once #3294 is implemented.

[a31amit]

While this can be a per-user basis, adding a new default global configuration options would also help to change global behaviors. currently, default is JSON without any option to configure in configuration.py.

[jeremystretch]

A per-user toggle for this would be sufficient. We want to avoid clogging up the global configuration with niche toggles.