[REQ][PHP] Add minimal CI config to PHP generators

[ybelenko]

Is your feature request related to a problem? Please describe.

Recently noticed how many PHP based projects migrates from Travis-CI to GitHub Actions. I didn't try it yet, but after a quick reading I see that GitHub Actions has Ubuntu environment with preinstalled PHP from 7.4 to 8.1, while Travis CI offers Bionic Env with PHP 7.4 only. It can speed up tests significantly I guess.

Since I never used other CI tools but Travis CI, I would ask our community to share their practices regarding PHP CI. If somebody can drop a config to test generated samples under PHP 7.4, 8.0 and 8.1 via GitHub hosted runners I would much appreciate that.

Describe the solution you'd like

• Remove Travis CI config from current repo and from all PHP based generators samples.
• Setup GitHub Actions to autotest PHP based generators also add basic config to samples.

Describe alternatives you've considered

Suggest other tool if GitHub Actions doesn't fit.

Additional context

This might be a good first issue for new contributors since you don't need to know Java.

cc @jebentier @dkarlovi @mandrean @jfastnacht @ackintosh @renepardon
active PHP contributor @Articus

[Articus]

I would ask our community to share their practices regarding PHP CI

Github Actions is more versatile than just a predefined environment - it allows to execute CI scenario inside a Docker container launched from any custom image. And that is exactly how I use it right now to run tests for my libraries against different PHP versions - I prepared a single Dockerfile to build 6 images (one for each supported PHP version - from 7.1 to 8.1) and added single workflow that uses build matrix to run tests in 6 containers concurrently. All images are stored in Github Container Registry. Here is a working example if you want one.