[9.x] Support PHP 8.0

[driesvints]

This provides support for PHP 8 so people on Laravel 6 LTS can still install Passport. Unfortunately this requires the dropping of PHP 7.2 support because OAuth2 Server v8.2 dropped it as well.

An alternative solution to the issues for people on Laravel 6 LTS and keep PHP 7.2 support is to constrain lcobucci/jwt to <=3.3. but that then we won't be able to offer PHP 8 support on Passport 9.

@taylorotwell I'll leave it up to you to decide on this.

Thanks to @Sephster PHP 7.2 was re-added to OAuth2 Server 8 🎉

[Sephster]

I dropped PHP 7.2 support because it is almost out of security release support. I think it only has a couple of days left before it is fully unsupported. However, there is no technical reason for this. If it is helpful, I can change the release to re-add PHP 7.2 for ease if it is going to cause you issues so there is another option for you if needed 👍

[driesvints]

@Sephster I think your choice for dropping PHP 7.2 is a sensible one and one we can also make here. Let's see what @taylorotwell says 🙂

[driesvints]

@velkymx you're not really contributing anything productive to this discussion. Please be patient until we're ready with this PR. We're close to merging and releasing this.