[CLI] Add qmk list_keyboards (#6927)

`list_keyboards` replicates the `make list-keyboards` by globbing for all paths
that include `rules.mk` and then removing the paths that include `keymaps`.

This basis of this cli command could be reused in the future as a util, but is
not done so here since this would be the only place that would use it currently

Resolves #6911

lib/python/qmk/cli/__init__.py

@@ -8,6 +8,7 @@ from . import config
 from . import doctor
 from . import hello
 from . import json
+from . import list
 from . import new
 from . import pyformat
 from . import pytest

lib/python/qmk/cli/list/__init__.py

@@ -0,0 +1 @@
+from . import keyboards

lib/python/qmk/cli/list/keyboards.py

@@ -0,0 +1,26 @@
+"""List the keyboards currently defined within QMK
+"""
+import os
+import re
+import glob
+
+from milc import cli
+
+@cli.subcommand("List the keyboards currently defined within QMK")
+def list_keyboards(cli):
+    """List the keyboards currently defined within QMK
+    """
+
+    base_path = os.path.join(os.getcwd(), "keyboards") + os.path.sep
+    kb_path_wildcard = os.path.join(base_path, "**", "rules.mk")
+
+    # find everywhere we have rules.mk where keymaps isn't in the path
+    paths = [path for path in glob.iglob(kb_path_wildcard, recursive=True) if 'keymaps' not in path]
+
+    # strip the keyboard directory path prefix and rules.mk suffix and alphabetize
+    find_name = lambda path: path.replace(base_path, "").replace(os.path.sep + "rules.mk", "")
+    names = sorted(map(find_name, paths))
+
+    for name in names:
+        # We echo instead of cli.log.info to allow easier piping of this output
+        cli.echo(name)