Running on OpenShift

Could not find any documentation for running `envbuilder` on OpenShift even though it is mentioned that it can run on it.
When trying to run on OpenShift, I'm getting:

```
error: running command "envbuilder": compile devcontainer.json: open dockerfile: open /.envbuider/Dockerfile: permission denied
```

Start by reviewing the existing envbuilder documentation and reproducing the reported envbuilder command on OpenShift. Document the supported OpenShift setup and explain how to address the permission-denied error for /.envbuider/Dockerfile; done when a user can follow the documentation to run envbuilder successfully.

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