feat: mark the "promote-bundle" command as deprecated (canonical#2226)

This command is deprecated and will be removed in Charmcraft 4.0. Bundle
commands will remain available in Charmcraft 3.

CRAFT-4005

Author: lengau

charmcraft/application/commands/store.py

@@ -1037,6 +1037,11 @@ def fill_parser(self, parser: "ArgumentParser") -> None:
 
     def run(self, parsed_args: "Namespace") -> None:
         """Run the command."""
+        emit.progress(
+            "Bundle commands are deprecated and will be removed in Charmcraft 4.",
+            permanent=True,
+        )
+
         if not isinstance(self._services.project, project.Bundle):
             raise CraftError("promote-bundle must be run on a bundle.")