adding contact and badge for pytest-dev discord server (#9078)

* adding badges/docs for pytest-dev discord and pytest libera web chat

doc/en/contact.rst

@@ -8,6 +8,8 @@ Contact channels
 - `pytest issue tracker`_ to report bugs or suggest features (for version
   2.0 and above).
 - `pytest discussions`_ at github for general questions.
+- `pytest discord server <https://discord.com/invite/pytest-dev>`_
+  for pytest development visibility and general assistance.
 - `pytest on stackoverflow.com <http://stackoverflow.com/search?q=pytest>`_
   to post precise questions with the tag ``pytest``.  New Questions will usually
   be seen by pytest users or developers and answered quickly.