Document design mode and enabling deployment mode

[alhogan]

Environment

• Nautobot version: >=2.2.0, <3.0.0
• nautobot-design-builder version: 2.2.0

Proposed Functionality

• Document the design_mode Class Metadata attribute
• Document how to enable deployment mode with best practices

Use Case

• The docs should clearly guide users on how to enable and use deployment mode