feat: add --commit-prompt switch

The new `--commit-prompt` switch allows users to specify a custom prompt for generating commit messages. This feature is implemented by adding the new argument to the argument parser in `aider/args.py` and passing it to the `Coder.create` method in `aider/main.py`.

aider/args.py

@@ -352,6 +352,11 @@ def get_parser(default_config_files, git_root):
         default=False,
         help="Prefix commit messages with 'aider: ' (default: False)",
     )
+    group.add_argument(
+        "--commit-prompt",
+        metavar="PROMPT",
+        help="Specify a custom prompt for generating commit messages",
+    )
     group.add_argument(
         "--dry-run",
         action=argparse.BooleanOptionalAction,

aider/main.py

@@ -490,6 +490,7 @@ def main(argv=None, input=None, output=None, force_git_root=None, return_coder=F
             attribute_committer=args.attribute_committer,
             attribute_commit_message=args.attribute_commit_message,
             verify_ssl=args.verify_ssl,
+            commit_prompt=args.commit_prompt,
         )
 
     except ValueError as err: