feat(phpstan): add support for phpstan

[damienwebdev]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/graycoreio/github-actions-magento2/blob/main/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Currently, we don't support using phpstan so we have less static analysis than we possibly could.

Fixes: N/A

What is the new behavior?

We use phpstan and @shochdoerfer 's https://github.com/bitExpert/phpstan-magento to statically analyze Magento further.

However, for backwards compatability, this task is disabled by default. It will likely become enabled in the future. Users can opt-in by adding one of the following (depending on what you're trying to do):

Check Store

.github/check-store.json

{
  "$schema": "https://raw.githubusercontent.com/graycoreio/github-actions-magento2/main/resolve-check-config/check-store.schema.json",
  "jobs": {
    "phpstan": true
  }
}

Check Extension

.github/check-extension.json

{
  "$schema": "[../resolve-check-config/check-extension.schema.json](https://raw.githubusercontent.com/graycoreio/github-actions-magento2/main/resolve-check-config/check-extension.schema.json)",
  "jobs": {
    "phpstan": true
  }
}

Does this PR introduce a breaking change?

• Yes
• No

Other information