Optional ability to set the pypi repository and credentials to be used by pip on the runner

Description:
Add option with flags to allow users of the action to setup a pip.conf or pip.ini file with a private registry and credentials.

Example usage:

 - name: Set up Python ${{ matrix.python-version }}
     uses: actions/setup-python@v5
      with:
        python-version: ${{ matrix.python-version }}
        repository: ${{ secrets.PYPI_REPO_URL }}
        username: ${{ secrets.PYPI_USER_TOKEN }}
        password: ${{ secrets.PYPI_PASS_TOKEN }}
    - name: Install dependencies
      run: |
        python -m pip install --upgrade pip
        pip install -r requirements.txt

Justification:
Using this action on ephemeral runners in environments where where companies have their own repository's to cache python dependencies. Great example (and my use case) is an enterprise nexus pypi repo where the open source pypi is blocked by firewall and dependencies need to be security scanned and placed in nexus prior to use internally. Having one setup-python action run and have the runner configured properly to use pip in any environment prevents the clutter having to manually write a pip.conf/pip.ini file every time we want to pip install.

Are you willing to submit a PR?
Absolutely, I am new to typescript but would love to put in a PR if others agree the work is useful.

首先查看 setup-python action 现有的 inputs 和 runner 设置流程，然后确定如何为私有仓库和凭据配置 pip.conf 或 pip.ini。完成标准是该 action 能够接受所需的仓库和凭据 inputs，为后续安装配置 pip，并在受支持的 runner 环境中验证其行为。