add default_persistence_allowed

In addition set all config options in every test, as catch2 can run
tests out of order and as demonstrated in
e1ad60af4f this can be an issue

CHANGELOG.rst

@@ -19,8 +19,9 @@ For admins
 ----------
 - Command line option --test-config (or -t) has been added. When used,
   biboumi will just exit without any error if the configuration is correct
-- Options persist_user_denylist and persist_user_allowlist have been added to
-  granualy control who can set the persist option
+- Options default_persistence_allowed, persist_user_denylist, and
+  persist_user_allowlist have been added to granualy control who can set the
+  persist option
 
 For packagers
 -------------