Handling packages unabled to be installed via repo2docker

[celine168]

Based on the issue raised in https://libretexts-constructionforum.groups.io/g/jupyter/topic/75068383, where a writer requested Octave 5.2 on our default environment for a LibreTexts textbook.

Octave 5.2 is only available via apt on Ubuntu 20.04 and not on Ubuntu 18.04. Repo2docker currently uses Ubuntu 18.04, although there are talks to eventually move to 20.04 or give the option for users to specify so (draft PR and related issue).

I'm creating this issue to discuss how we should handle this case and cases like these in the future, where repo2docker may not give the features/packages that LibreTexts users may want. If this issue becomes common, we may want to prioritize #85 and allow users to create their own repo2docker/Dockerfiles as environments.

[moorepants]

I think we should stick to supporting only the packages available in 18.04 APT or via conda (conda-forge channel). We have a couple special cases: sage, julia right now, but those will eventually work smoothly from conda installs. Octave can also be installed via conda but last time I tried it didn't work.

[moorepants]

And yes, I see #85 as the solution for users that need something we don't support. For this Octave 5.2 issue though, solving #85 is a lot of work for adding one function to the user space.

[moorepants]

We determined that repo2docker is staying on 18.04 for now, so we will have to stick to those APT packages. If conda-forge's octave package is updated (or we update it), then we could use that.

[sandertyu]

Octave is available through conda-forge but it is on an older version than what we install through apt. Additionally, most of the octave packages are not available through conda-forge, so we would have to find some other way to install them. For now, it is probably best to stick with apt.

[moorepants]

We stick to what we can install with repo2docker. Users can install manually otherwise. Closing.