CI setup and jdk8 fixes #4
Description
The application is having trouble working due to changes in Maven central policy, tests are failings when executing a mvn verify command on a workstation.
Setting up a CI will help identify the issues and future developments. Using only a jdk8 for the moment seems to be a good start to make it back on track. This could fix errors displayed in restx/restx#327.
Adding a jdk11 job like in restx project could be done in a second issue to start a java 11 migration.