feat(cli): define the agency top-level command

    benefits agency -h

benefits/cli/management/commands/agency.py

@@ -0,0 +1,12 @@
+from benefits.cli.commands import BenefitsCommand
+
+
+class Command(BenefitsCommand):
+    """Work with transit agencies."""
+
+    help = __doc__
+    name = "agency"
+    subcommands = []
+
+    def __init__(self, stdout=None, stderr=None, no_color=False, force_color=False):
+        super().__init__(stdout, stderr, no_color, force_color)

tests/pytest/cli/management/commands/test_agency.py

@@ -0,0 +1,18 @@
+import pytest
+
+from benefits.cli.management.commands.agency import Command
+
+
+@pytest.mark.django_db
+def test_class():
+    assert Command.help == Command.__doc__
+    assert Command.name == "agency"
+    assert Command.subcommands == []
+
+
+@pytest.mark.django_db
+def test_init():
+    cmd = Command()
+
+    assert "agency" in cmd.subparsers
+    assert cmd.subparser == cmd.subparsers["agency"]