automatically run black on files we update via templates

sometimes filling in a template leads to black changes (when an URL
makes a line too long, for example), so lets fix that directly when
generating, avoiding a second "black" commit

Author: evgeni

plugin-template

@@ -5,6 +5,7 @@ import os
 import pprint
 import shlex
 import shutil
+import subprocess
 import sys
 import textwrap
 from pathlib import Path
@@ -402,6 +403,14 @@ def write_template_section(config, name, plugin_root_dir, verbose=False):
             files_copied += 1
             if verbose:
                 print(f"Copied file: {relative_path}")
+        if config["black"] and destination_relative_path.endswith((".py", ".py.j2")):
+            if destination_relative_path.endswith(".py.j2"):
+                destination = destination_relative_path[: -len(".j2")]
+            else:
+                destination = destination_relative_path
+
+            if os.path.exists(os.path.join(plugin_root_dir, destination)):
+                subprocess.run(["black", "--quiet", destination], cwd=plugin_root_dir)
 
     print(f"Section: {name} \n    templated: {files_templated}\n    copied: {files_copied}")
     return 0