Add option to create a new branch

Description

Add a New Branch action to the Graph section in the sidebar.

Proposed workflow

1. Choose the base branch: Provide two options:

   • Use main as the base branch (default).
   • Select another existing branch as the base.

2. Handle current changes: If there are uncommitted changes, ask the user whether to bring them into the new branch or leave them in the current branch.

3. Create the branch: Create the new branch using the selected base branch and handle the current changes according to the user's choice.

This would make branch creation more convenient and give users control over the base branch and their existing changes.