Update pip install documentation in recipes for dependencies and build isolation

[riccardoporreca]

Checklist

• I added a descriptive title
• I searched open requests and couldn't find a duplicate

What is the idea?

We find many recipes around that use pip install --no-deps . -vv in build scripts, which is also documented in many places for conda-build.

However, pip dependencies, as well as build isolation, are completely disabled via environment variables by conda-build itself, see https://github.com/conda/conda-build/blob/3.25.0/conda_build/build.py#L3163-L3183

Why is this needed?

To make users of conda-build and maintainers of conda recipes aware of the pip configuration done by conda-build under the hood and suggest a simple pip install . -vv in build scripts

What should happen?

Documentation and examples updated

See https://github.com/search?q=repo%3Aconda%2Fconda-build+%22pip+install%22+%22--no-deps%22&type=code

Additional Context

No response

[riccardoporreca]

Happy to help out and draft a PR

[riccardoporreca]

@kenodegard, I stumbled over #4960, which seems to go in quite the opposite direction compared to what I was bringing up here...

[github-actions]

Hi there, thank you for your contribution!

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