Docs: Update doc for Viewset lookup field to note that UI elements may be missing

[scetron]

Environment

• Nautobot version (Docker tag too if applicable): 1.5.10 / latest docs
• Python version: n/a
• Database platform, version: n/a
• Middleware(s): n/a

Steps to Reproduce

Expected Behavior

Docs should specify caveats of changing lookup field.

Observed Behavior

Docs don't mention using id or other lookup fields over using pk or slug. Viewset router is looking for key pk rather than id to assemble URLs which makes buttons not show up on object detail (retrieve) screens.

[smk4664]

This already exists the documentation: https://docs.nautobot.com/projects/core/en/stable/plugins/development/?h=lookup_field#setting-viewset-attributes

Also, the Example Plugin makes use of this.

[scetron]

The documentation is not specific enough.