Pin Markupsafe until we are able to upgrade Flask/Jinja

Markupsafe 2.1.0 breaks with error: import name 'soft_unicode' from 'markupsafe'.
This should be removed when either this issue is closed:
pallets/markupsafe#284
or when we will be able to upgrade JINJA to newer version (currently
limited due to Flask and Flask Application Builder)

setup.cfg

@@ -133,7 +133,12 @@ install_requires =
     lazy-object-proxy
     lockfile>=0.12.2
     markdown>=3.0
-    markupsafe>=1.1.1
+    # Markupsafe 2.1.0 breaks with error: import name 'soft_unicode' from 'markupsafe'.
+    # This should be removed when either this issue is closed:
+    # https://github.com/pallets/markupsafe/issues/284
+    # or when we will be able to upgrade JINJA to newer version (currently limited due to Flask and
+    # Flask Application Builder)
+    markupsafe>=1.1.1,<2.1.0
     marshmallow-oneofschema>=2.0.1
     packaging>=14.0
     pendulum>=2.0