feat: allow extensions to add commands (#1017)

* feat: allow extensions to add commands

* refactor: fix tests

* refactor: more test fix

* refactor: more test fixes

* refactor: more linter fixes

tests/test_command_components.py

@@ -0,0 +1,66 @@
+from io import StringIO
+from unittest.mock import patch
+
+from django.core.management import call_command
+from django_components.testing import djc_test
+from .testutils import setup_test_config
+
+setup_test_config({"autodiscover": False})
+
+
+@djc_test
+class TestComponentCommand:
+    def test_root_command(self):
+        out = StringIO()
+        with patch("sys.stdout", new=out):
+            call_command("components")
+        output = out.getvalue()
+
+        # NOTE: The full output is different in CI and locally, because of different whitespace wrapping
+        # (probably due to different terminal widths). So we check only for parts of the output.
+        #
+        # The full expected output is:
+        # ```
+        # usage: components [-h] [--version] [-v {{0,1,2,3}}] [--settings SETTINGS] [--pythonpath PYTHONPATH]
+        #                   [--traceback] [--no-color] [--force-color] [--skip-checks]
+        #                   {{create,upgrade,ext}} ...
+        #
+        # The entrypoint for the 'components' commands.
+        #
+        # optional arguments:
+        #   -h, --help            show this help message and exit
+        #   --version             Show program's version number and exit.
+        #   -v {{0,1,2,3}}, --verbosity {{0,1,2,3}}
+        #                         Verbosity level; 0=minimal output, 1=normal output, 2=verbose output,
+        #                         3=very verbose output
+        #   --settings SETTINGS   The Python path to a settings module, e.g. "myproject.settings.main". If this
+        #                         isn't provided, the DJANGO_SETTINGS_MODULE environment variable will be used.
+        #   --pythonpath PYTHONPATH
+        #                         A directory to add to the Python path, e.g. "/home/djangoprojects/myproject".
+        #   --traceback           Raise on CommandError exceptions.
+        #   --no-color            Don't colorize the command output.
+        #   --force-color         Force colorization of the command output.
+        #   --skip-checks         Skip system checks.
+        #
+        # subcommands:
+        #   {{create,upgrade,ext}}
+        #     create              Create a new django component.
+        #     upgrade             Upgrade django components syntax from '{{% component_block ... %}}' to
+        #                         '{{% component ... %}}'.
+        #     ext                 Run extension commands.
+        # ```
+
+        assert "usage: components" in output
+        assert "The entrypoint for the 'components' commands." in output
+        assert "-h, --help            show this help message and exit" in output
+        assert "--version             Show program's version number and exit." in output
+        assert "-v {0,1,2,3}" in output
+        assert "--settings SETTINGS   The Python path to a settings module" in output
+        assert "--pythonpath PYTHONPATH" in output
+        assert "--traceback           Raise on CommandError exceptions." in output
+        assert "--no-color            Don't colorize the command output." in output
+        assert "--force-color         Force colorization of the command output." in output
+        assert "--skip-checks         Skip system checks." in output
+        assert "create              Create a new django component." in output
+        assert "upgrade             Upgrade django components syntax" in output
+        assert "ext                 Run extension commands." in output