Allow modules without the -module prefix using extra option

[bert-w]

Apparently there appears to be a requirement to name your repository in a specific way in order to be accepted as a Laravel module.

I've added a much more simple solution that allows to add an additional property to composer.json of any repository:

{
    "extra": {
        "module-dir-name": "MyModuleName"
    }
}

Then, together with

{
    "type": "laravel-module"
}

any repository should work.

This adds the most flexibility. I've also used the ?? operator (PHP 7+ which works for this package) to simplify the code.

PS: I coded this on Github so I didnt test it.

@nWidart possible doc update for https://nwidart.com/laravel-modules/v6/advanced-tools/publishing-modules if this gets accepted?

[bert-w]

@joshbrw can you take a look at this PR? thx