PHP: Go async with AMP

[lennartdohmann]

Use AMPHP to go async

[unglaublicherdude]

I tested the implementation on an IONOS webhosting (shared-hosting) server and it does run there. 👍

[unglaublicherdude]

We ran into an issue with async php by using the revolt/eventloop (dependency of the amphp packgages).

The nextcloud-app fails (only in the ci) when updating the http-client to the amphp one.

There is an issue with the revolt/eventloop and opcache which we can workaround by deactivate the opcache for the vendor/amphp directory. But for now, we decided to don't put anymore effort into this.

I opened this revoltphp/event-loop#95.
I opened this amphp/http-client#365.

With this issue, this PR is also basically obsolete too.

What we still have to do is to revert the http-client to the guzzle one or to build a factory that creates an http-client regarding to some ini-settings (opcache.enabled would lead to good old guzzle).