Phpdev async with amphp

[unglaublicherdude]

So basically you can now require a specific branch.

Branches that are named like phpdev-* are pushed without the phpdev- prefix to the vaas-php repository.

So when you have a branch called phpdev-somethinggreat you can install the branch with

composer require gdata/vaas:dev-somethinggreat

[unglaublicherdude]

This PR also replaces this https://github.com/GDATASoftwareAG/vaas/pull/544

[unglaublicherdude]

You can see the asnyc version running in this https://github.com/GDATASoftwareAG/nextcloud-gdata-antivirus/pull/117

[unglaublicherdude]

This has to be a major release because there is a big api change

[unglaublicherdude]

will merge this, after the wordpress-review is passed