fix: Use root-binaries conda-forge package as build base

[matthewfeickert]

• Resolves root_base based build doesn't have root in PATH #4
• Needed by pyhf/pyhf-validation PR 9

As (pointed out by @kratsg) root_base doesn't doesn't copy any of the compiled C++ code over, a build that is based on root_base won't actually have a working ROOT installation (though PyROOT will work). As a result of this, base the build around the conda-forge package root-binaries instead which does include a ROOT runtime.

The current root_base based image is 551.49 MB compressed, and this root-binaries build is 568.43 MB compressed, so I think the size increase isn't too bad.

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• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

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For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Base build around conda-forge 'root-binaries' to get ROOT runtime
* Add checks to build CI for ROOT, hist2workspace, and common utilities

[matthewfeickert]

@henryiii and @chrisburr, if you have suggestions on additional libs to remove that would be welcome info.