Camel 4.4 - Allow to configure camel.variable.xxx

[davsclaus]

Describe the feature here

Camel 4.4 introduced variables which can be configured from application.properties.
https://issues.apache.org/jira/projects/CAMEL/issues/CAMEL-19749

However for Quarkus and Spring Boot then this requires to add code to support this

A SB example is at
https://github.com/apache/camel-spring-boot-examples/tree/main/variables

And the commit in SB to support this is:
apache/camel-spring-boot@671e772

[JiriOndrusek]

There are 3 parts of the solution:

1. Code in the camel-quarkus main: which is already merged in the camel-main branch as a part of upgrade to Camel 4.4
2. Basic test coverage: Variables - test coverage #5654
3. Example: Variables example camel-quarkus-examples#194