doc/mgr: update prompts in dboard.rst includes

doc/mgr: update prompts in dboard.rst includes

This PR adds unselectable prompts to three files that are
transcluded in the doc/mgr/dashboard.rst file. These three
files are:

 1. debug.inc.rst
 2. feature_toggles.inc.rst
 3. motd.inc.rst

The addition of unselectable prompts to these three files
completes the work begun in PR#47810 (d8064b4), which sought
to bring dashboard.rst into line with the unselectable prompt
standard introduced by Kefu Chai in 2020.

Signed-off-by: Zac Dover <zac.dover@gmail.com>