Replace Matrix link with Zulip (#966)

* Replace Matrix link/icon with Zulip

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Removing Zulip logo change, as that will happen at theme level

* Add sphinx configuration to ReadTheDocs file

* Fix config file after main merge

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: kathatherine

docs/source/help-support.rst

@@ -19,8 +19,8 @@ request new features, and submit any other comments you might have.
 
   .. grid-item::
 
-     .. card:: Conda Matrix chat
-        :link: https://matrix.to/#/#conda:matrix.org
+     .. card:: Conda Zulip chat
+        :link: https://conda.zulipchat.com
 
         Chat about conda issues and projects with other users