Add support for Alpine Linux

[geneh]

Details to be added.

[bduranc]

This topic was discussed previously on our Dec 16th, 2019 curation steering committee call and a relevant GH issue appears to have been previously opened here. I'd like to add my thoughts on this topic below:

Support for Alpine Linux packages would be beneficial to the ClearlyDefined ecosystem, particularly when it comes to improving container support because Alpine is a popular Linux distribution for Docker images.

The following repo https://git.alpinelinux.org/cgit/aports and it's mirror https://github.com/alpinelinux/aports/ contain manifests and build scripts for building different Alpine packages.

These packages consist of "APKBUILD" files which contain information required to build the packages from source. There are also sometimes additional "*.patch" files which may contain some source code. (See: https://wiki.alpinelinux.org/wiki/Creating_an_Alpine_package)

It appears one can browse built packages at https://pkgs.alpinelinux.org/packages from "main", "community", and "testing" repos and install them using the "apk" command (See: https://wiki.alpinelinux.org/wiki/Alpine_Linux_package_management).

I wouldn't call myself an expert with Alpine Linux, but the above was what I was able to investigate. Perhaps there may be others more experienced who can add additional clarification, detail, or other input. If we can get additional input from these folks, that may add additional value to this issue.

But I do see potential value if Alpine packages could exist as their own "type" in ClearlyDefined, along with the possibility to link them to their corresponding source code (but should it be in official project repo or Alpine's "aports"?).

@pombredanne: please let us know if you have any additional comments to add or if I am missing/forgetting something :) Apologies for the delay in posting this :(

Anyone else... please of course feel free to do the same.

Thanks.