Add OpenChain badge in AQA repo

[llxia]

AQAvit has achieved OpenChain 2.1 badge (see https://github.com/adoptium/adoptium.net/issues/2797). We can add the OpenChain 2.1 badge on https://github.com/adoptium/aqa-tests/blob/master/README.md

Image: https://github.com/OpenChain-Project/Image-Assets/tree/master/Official/Conformance-Badge

[llxia]

https://shields.io/docs/logos#custom-logos can be used for custom logo. We need to use base64 encoding.

[llxia]

I have tried to covert https://github.com/OpenChain-Project/Image-Assets/blob/master/Official/Conformance-Badge/OpenChain-License-Compliance-2.0/openchain-2-0.svg?short_path=74e172a to base64 encoding via https://fffuel.co/eeencode/. It did not work.