Set channel priority to strict, print config info

[nkaretnikov]

This PR sets the channel priority to strict to avoid issues during solves when multiple channels that were not specified are being used. This is done by passing the command line option --strict-channel-priority via the environment variable CONDA_FLAGS, which is used by conda-lock, which is a library conda-store uses to solve dependencies.

CONDA_FLAGS is used because it's a method of passing options that's local to conda-lock as opposed to editing global conda configuration files. Editing user configuration files may lead to unexpected issues in contexts where conda-store is used in standalone mode. Those configuration files affect how conda works outside of conda-store, which might be important to end users.

From the documentation at https://docs.conda.io/projects/conda/en/latest/user-guide/tasks/manage-channels.html:

With strict channel priority, packages in lower priority channels are not considered if a package with the same name
appears in a higher priority channel.

Additionally, this PR adds code that prints useful system information related to conda configuration before the package solving process. This is useful for debugging. The commands used are:

• conda/mamba info, depending on the value of conda_store.conda_command
• conda config --show
• conda config --show-sources.

Note that the latter two commands are not supported by mamba, which is why conda is used.

Fixes #359, fixes #659.

[netlify]

✅ Deploy Preview for kaleidoscopic-dango-0cf31d ready!

Name	Link
🔨 Latest commit	973a2a4
🔍 Latest deploy log	https://app.netlify.com/sites/kaleidoscopic-dango-0cf31d/deploys/65809a3f2cf0a400085656a2
😎 Deploy Preview	https://deploy-preview-693--kaleidoscopic-dango-0cf31d.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[trallard]

Thanks @nkaretnikov - I left a few comments and questions.
I generally do not like to use print for what should be logged or streamed, so unless there is a strong reason to use print this should be changed

[trallard]

Thank you, this LGTM 🚀 merging now!