Introduce static analysis

[szepeviktor]

Description

Run PHPStan in CI

References

#785

Testing

Ci does it.

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not master

[szepeviktor]

Could anyone help me fix the rest of errors ❔

[evansims]

Hey @szepeviktor 👋 Thanks for your work on this! I know you have this marked as a draft, but I went ahead and merged a lot of your valuable efforts here into master as I was already in the process of cleaning things up. I've merged those changes from master back to this PR to bring it up to date as a result. Will give you complete credit for your efforts here in the changelog, of course, it's really so appreciated!

Did you have additional efforts you wanted to pursue in this PR that we should leave it open for? Happy to do so, just wanted to check! Thank you again

[szepeviktor]

Thank you very much for your kind response.
This PR is actually an inspiration.
Please include PHPStan in your CI if you see its huge benefit.