[3.8] gh-91888: add a `:gh:` role to the documentation (GH-91889) (#91936)

[3.8] gh-91888: add a `:gh:` role to the documentation (GH-91889) (#91936)

* gh-91888: Add a :gh: role to the documentation (GH-91889).

* [3.8] gh-91888: add a `:gh:` role to the documentation (GH-91889)

* Add a new :gh:`...` role for GitHub issues.

* Fix a GitHub id to use the :gh: role.

* Add Misc/NEWS entry.

* Refactoring and rephrasing.

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>.
(cherry picked from commit f7641a2ffec243e5f600028a84debe9028a9ee44)

Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com>
* Fix use of the default role in NEWS entry