fix: do not end process in middleware mode, fix #4196

[IanVS]

Description

Fixes #4196.

It doesn't make much sense to end the vite process based on stdin when vite is running in middleware mode, as pointed out in #4196.

Additional context

I based the original check for CI off of what create-react-app does, but that project does not have a specific "middleware mode". I think it makes sense to include both of these checks, until/unless we can find a good way to detect running in docker/CI/container/non-interactive terminal (which is harder than it seems like it should be).

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.