onboarding: Fix topic names not being translated correctly.

In 'send_initial_realm_messages', the topics names were not
being translated properly as they were computed outside the
with `override_language` block.

Now, we use 'send_initial_realm_messages' inside a with
'override_language' block in the caller. This fixes the bug.

Note: We are using 'override_language' block in the caller
and not within the function as it helps to avoid indenting
everything inside the function.

zerver/actions/create_user.py

@@ -582,6 +582,7 @@ def do_create_user(
     if realm_creation:
         from zerver.lib.onboarding import send_initial_realm_messages
 
+        with override_language(realm.default_language):
             send_initial_realm_messages(realm)
 
     return user_profile

zerver/lib/onboarding.py

@@ -271,7 +271,6 @@ def send_initial_realm_messages(realm: Realm) -> None:
     # at least one message.
     welcome_bot = get_system_bot(settings.WELCOME_BOT, realm.id)
 
-    with override_language(realm.default_language):
     # Content is declared here to apply translation properly.
     #
     # remove_single_newlines needs to be called on any multiline