Add support for custom package generated with composer archive

[Elendev]

The command composer archive --format=zip generate a ZIP archive with the composer.json file at the root of the archive. The nexus-repository-composer is unable to handle this kind of archives correctly since it search for composer.json inside a subdirectory of the given archive. This PR modify the way the composer.json is fetched in the ZIP archive to allow to handle the archives generates by composer.

This pull request makes the following changes:

• Find the composer.json file even if it's on the root of the archive
• Add corresponding unit tests

It relates to the following issue :

• Fixes #26

[sonatypecla[bot]]

Thanks for the contribution! Before we can merge this, we need @Elendev to sign the Sonatype Contributor License Agreement.

[fjmilens3]

Thanks for putting this together, @Elendev! I don't have time to take a look at it right at the moment but we'll make sure we do.

Beyond that, I would suggest that you add your name to the contributors file as part of this PR! :)

[Elendev]

@fjmilens3 done, I've added myself to the contributor list :-)

[HabibMAALEM]

Hi guys, @fjmilens3 can you approve this PR to finish the merge

[fjmilens3]

@Elendev, made a few very minor (and pedantic) code style and formatting notes. Once those are changed I'm comfortable with merging this down, thanks for putting it together.

@HabibMAALEM, see the above comments, we should be able to get this merged in shortly.

@TheBay0r, if you're interested, you may want to give this a quick test yourself as our unofficial QA expert as well. I don't think it's exactly the riskiest change in the world, however!

[TheBay0r]

@fjmilens3 I'll have a look either today or Monday 👍

[TheBay0r]

I just had a look. I was able to reproduce the initial issue and it seems it is fixe with this branch. Also regression seems fine! Looks good from my point of view 👍

[Elendev]

@fjmilens3 I've fixed the typo and the formatting issues