added list of tlmgr packages to install as data

[ttimbers]

Based on the conversation in #228 I am submitting this pull request to add a data object named jup_pkgs so that the additional packages required for using {tinytex} with Jupyter can be installed via:

tinytex::install_tinytex(extra_packages = tinytex::jup_pkgs)

A couple of notes:

• A separate doc PR will need to be sent to yihui/yihui.org to communicate that this exists and how to install {tinytex} to get these packages installed. Can you point me to where you would like this added there in the {tinytex} docs?
• I am not sure if/how tests should be made for this contribution. Suggestions/direction welcome.
• What if folks wanted this for Jupyter only, similar to folks who might use the For Other Users approach? Where should I add this list of packages to make this work? I guess an optional bash shell argument for the tools/install-unx.sh script would work for example?

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