Improve command system; add aliases for commands (#2635)

* Command name supports multiple names

* Separate CommandRegistry.commands and .command_aliases

* Update test_commands.py

* Add __contains__ operator to CommandRegistry

* Update error message for unknown commands

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Co-authored-by: Reinier van der Leer <github@pwuts.nl>

tests/unit/test_execute_command.py

@@ -8,17 +8,16 @@ def check_plan():
 
 def test_execute_command_plugin(agent: Agent):
     """Test that executing a command that came from a plugin works as expected"""
+    command_name = "check_plan"
     agent.ai_config.prompt_generator.add_command(
-        "check_plan",
+        command_name,
         "Read the plan.md with the next goals to achieve",
         {},
         check_plan,
     )
-    command_name = "check_plan"
-    arguments = {}
     command_result = execute_command(
         command_name=command_name,
-        arguments=arguments,
+        arguments={},
         agent=agent,
     )
     assert command_result == "hi"