Add tests to the oauth2 quickstart

[cescoffier]

• Add Quarkus tests
• Add native tests

[cemnura]

Hello @cescoffier,

I had a poke on this and would love for you to review. I am creating a pull request.

Also I noticed that there is a documentation request on oauth2 topic #521 which I was thinking to include with the quarkus test for security-oauth2-quickstart that I would also want to work on.

[cescoffier]

Thanks, I will have a look today or tomorrow.

[cemnura]

Thanks. I will be looking forward to your review.