[Camel and Hippo] Demo project doesn't work in v12

The demo currently doesn't work.

Unfortunately, the demo sub-project was not upgraded to be compliant with v12 yet. The parent root pom (demo/pom.xml) still inherits from 10.1.0.

Tonny reported, discussed and solved collectively in community forum [1] recently. The information shared there would help fix the issue.

[1] https://community.bloomreach.com/t/does-camel-events-support-really-support-for-hippo-cms-12-x/306