Dockerfile openlibrary user should have fixed UID/GID

Our olbase Dockerfile creates an `openlibrary` user and group. These are assigned a new ID automatically by the container's OS. However this ID can conflict with users that exist on the host OS, creating potential security holes (I think?). Let's pick a UID/GID and specify it when creating the users in the container, and also let's do the same on the host machines in our provisioning scripts. (Which _I believe_ is the best practice?? Or maybe we only need this if we're mounting host folders onto the container, like we did for covers?)

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