[openthread_border_router] Make configure COAP an option in the add-on GUI

[rwrozelle]

What type of request is this?

Enhancement to existing add-on

Existing add-on name

OpenThread Border Router

Describe the add-on or add-on enhancement

I'd like to optionally enable COAP by having a front-end option flip the include flag OT_COAP from OFF to ON

Use cases

I am investigating using COAP for communication on a SED and need the OTBR to also have COAP enabled.

Upstream project

No response

Anything else?

No response