AsyncAPI spec v3 support in Java spring cloud stream template

[jonaslagoni]

Reason/Context

This Issue is used to track changes needed to support AsyncAPI v3. As a code owner, please edit this list of TODO tasks in order to properly track the progress 🙂 Once this issue is closed it means that v3 is now fully supported in this library.

Remaining tasks:

• [ ] Update template to use parser v2, this is already supported by the generator by changing the apiVersion