Add recipe/conda_build_config.yaml to use vs2017

[eriknw]

Checklist

• Used a personal fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
• [ ] Reset the build number to 0 (if the version changed)
• Re-rendered with the latest conda-smithy (Use the phrase @conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• Ensured the license file is being packaged.

I think recipe/conda_build_config.yaml is the correct way to specify which compiler to use:
https://conda-forge.org/docs/maintainer/knowledge_base.html#using-vs2019

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[eriknw]

@conda-forge-admin, please rerender

[github-actions]

Hi! This is the friendly automated conda-forge-webservice.

I tried to rerender for you, but it looks like there was nothing to do.

This message was generated by GitHub actions workflow run https://github.com/conda-forge/graphblas-feedstock/actions/runs/3275960735.

[eriknw]

This is a followup to #45, where I manually forced vs2017. This PR adds a config file so rerender should be correct and use vs2017 instead of updating to vs2019.