Add a `composer.json` file to make it consumable from php packages

[st3iny]

It would be nice if we could make the processed zones.json file available to the php ecosystem as well.

cc @SebastianKrupinski

[SebastianKrupinski]

If you could make that happen that would be great! I actually don't have access to the libraries.

On a side note if we could make the update script also generate a zones.php file this would make it even better as we couldn't need to de-serialize it for every request.