recent-topics: Update hash for view to be "#recent".

Updates the hash used for the recent conversations view to be
"#recent" instead of "#recent_topics".

We will need to keep the logic for handling "#recent_topics"
permanently because users potentially have messages from
Welcome Bot with links to that hash.

Including "recent_topics" as a web_public_allowed_hash in
hash_util.js can be changed once self-hosted servers cannot
upgrade directly to Zulip 5.x from the current version.

Fixes #23132.

zerver/lib/onboarding.py

@@ -154,7 +154,7 @@ def select_welcome_bot_response(human_response_lower: str) -> str:
                 )
                 + "\n\n",
                 _(
-                    "Check out [Recent conversations](#recent_topics) to see what's happening! "
+                    "Check out [Recent conversations](#recent) to see what's happening! "
                     'You can return to this conversation by clicking "Private messages" in the upper left.'
                 ),
             ]

zerver/tests/test_tutorial.py

@@ -98,7 +98,7 @@ class TutorialTests(ZulipTestCase):
             expected_response = (
                 "In Zulip, topics [tell you what a message is about](/help/streams-and-topics). "
                 "They are light-weight subjects, very similar to the subject line of an email.\n\n"
-                "Check out [Recent conversations](#recent_topics) to see what's happening! "
+                "Check out [Recent conversations](#recent) to see what's happening! "
                 'You can return to this conversation by clicking "Private messages" in the upper left.'
             )
             self.assertEqual(most_recent_message(user).content, expected_response)