feat: add support for the new commit_prompt arg to override prompts.commit_system

The GitRepo class in the aider/repo.py file has been updated to support a new `commit_prompt` argument. This allows overriding the default `prompts.commit_system` when generating commit messages.

The changes include:

1. Adding the `commit_prompt` parameter to the `__init__` method of the `GitRepo` class.
2. Storing the `commit_prompt` value in the `self.commit_prompt` attribute.
3. Modifying the `get_commit_message` method to use the `self.commit_prompt` value if it's provided, otherwise falling back to the default `prompts.commit_system`.

This change provides more flexibility in customizing the commit message generation process, allowing users to provide their own custom prompts if needed.

aider/repo.py

@@ -26,6 +26,7 @@ class GitRepo:
         attribute_author=True,
         attribute_committer=True,
         attribute_commit_message=False,
+        commit_prompt=None,
     ):
         self.io = io
         self.models = models
@@ -33,6 +34,7 @@ class GitRepo:
         self.attribute_author = attribute_author
         self.attribute_committer = attribute_committer
         self.attribute_commit_message = attribute_commit_message
+        self.commit_prompt = commit_prompt
 
         if git_dname:
             check_fnames = [git_dname]
@@ -154,8 +156,9 @@ class GitRepo:
             content += context + "\n"
         content += diffs
 
+        system_content = self.commit_prompt or prompts.commit_system
         messages = [
-            dict(role="system", content=prompts.commit_system),
+            dict(role="system", content=system_content),
             dict(role="user", content=content),
         ]