Add -m parameter to `git flow feature finish` for custom commit messages

[DyByronWu]

Summary

The git flow feature finish command currently does not support a -m parameter for specifying a custom commit message when merging a feature branch. Introducing this parameter would enable users to provide a specific message for the merge commit, enhancing the clarity and usefulness of the commit history.

Expected Behavior

A new -m or --message parameter should be available for the git flow feature finish command, allowing users to specify a custom commit message.
For example: git flow feature finish -m "Custom commit message"

Proposal

Add a -m or --message parameter to the git flow feature finish command. This parameter should accept a string input that will be used as the commit message for the merge commit when finishing the feature branch.

Benefits

• Improves commit history readability by allowing custom commit messages.
• Provides more flexibility and control to users over their commit messages.
• Aligns with common practices in other Git workflows that allow specifying commit messages.