topic: Add a first-time explanation for "Resolve topic".

We show a confirmation dialog explaining the "resolve topics"
feature when the user marks a topic resolved for the first time.
If the user confirms the action, we mark the
topic resolved, else we don't.

We don't show anything the first time a topic is marked
unresolved.

Fixes #31242

zerver/lib/onboarding_steps.py

@@ -52,6 +52,9 @@ ONE_TIME_NOTICES: list[OneTimeNotice] = [
     OneTimeNotice(
         name="interleaved_view_messages_fading",
     ),
+    OneTimeNotice(
+        name="intro_resolve_topic",
+    ),
 ]
 
 ONE_TIME_ACTIONS = [OneTimeAction(name="narrow_to_dm_with_welcome_bot_new_user")]