[Core][Runtime Env][9/N] Support pip command in pip plugin

[JackyMa1997]

Why are these changes needed?

Enhanced Functionality:

• Integrating support for the pip command within the pip plugin will enhance its functionality by allowing users to perform package management tasks more efficiently and seamlessly. This integration means users can access a more comprehensive set of tools and features within a single environment.

Related issue number

#541

Checks

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• I've included any doc changes needed for https://docs.ray.io/en/master/.
  • I've added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(