Feature: Add current branch name substitution in commit prompt

[thomasmison]

This PR add current branch name substitution in commit message prompt template

Example of usage:

  You are an expert software engineer that generates concise, \
  one-line Git commit messages based on the provided diffs.
  Review the provided context and diffs which are about to be committed to a git repo.
  Review the diffs carefully.
  Extract the task number from the branch name (e.g., from 'feature/san-8-XXXX' extract '8').
  Generate a one-line commit message for those changes.
  The commit message should be structured as follows: (<task_number>) <type>: <description>
  Use these for <type>: fix, feat, build, chore, ci, docs, style, refactor, perf, test

  Ensure the commit message:
  - Include task number in parentheses at the start (e.g., "(8)") from current branch name
  - Starts with the appropriate type prefix after the task number
  - Is in the imperative mood (e.g., "Add feature" not "Added feature" or "Adding feature")
  - Does not exceed 72 characters including the task number

  Reply only with the one-line commit message, without any additional text, explanations, \
  or line breaks.

  current branch name: {{branch_name}}

[paul-gauthier]

Thanks for your interest in aider and for preparing this PR.

Unfortunately, I don't understand why it is desirable to have the current branch name in the commit message prompt?

Also, are you aware that you can customize the commit message prompt with --commit-prompt switch/config?

https://aider.chat/docs/git.html#commit-messages