Add support for dependency relationships for alpine (apk)

[luhring]

Partially addresses #572

[spiffcs]

@tgerla I took this out of draft - if you push your changes I can review

[tgerla]

Hi @spiffcs (and anyone else interested) -- I think this one is ready to go. Can you please review my last commit, "adjust test conditions"? I think I've updated the test correctly, but I am Go noob.

[kzantow]

It looks like there are a couple // TODOs that might be important to fill out on this one -- what do you think?

[spiffcs]

Added a question about schema change procedure as well as separator being used. When we settle on the right separator we might want to add a quick test to be sure the split is behaving correctly.

Also small nit on the strings usage

splits := strings.Split(provides, "=")
if strings.Contains(splits[0], "=") {
    // protect against unsuccesful split
}

[wagoodman]

@tgerla it looks like there may be more things that were not originally in scope that need to be considered as part of this PR. It looks like the https://wiki.alpinelinux.org/wiki/Apk_spec page got a really healthy update over the last few months to help interpret an APK index vs installed DB file, which will be really helpful for determining the missing bits. I'd be happy to pair on this.

[kzantow]

Just a few non-blocking questions...

[luhring]

This one should not have been squashed 😄