Add API endpoint to retrieve configuration properties

[apeiris]

Added a new API endpoint to retrieve configuration properties from the config.xml file.

Changes

• Created an endpoint at /api/config/properties to return configuration properties as JSON.

Testing

• Verified the endpoint returns the correct JSON structure as expected.
  -Added unit testclass ApiResourceTest

[uhurusurfa]

Looks good.

[uhurusurfa]

It is failing because the jakarta package does not support Java 8.

[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /home/runner/work/OpenAs2App/OpenAs2App/Server/src/test/java/org/openas2/ApiResourceTest.java:[4,26] cannot access jakarta.ws.rs.core.Response
bad class file: /home/runner/.m2/repository/jakarta/ws/rs/jakarta.ws.rs-api/3.1.0/jakarta.ws.rs-api-3.1.0.jar(jakarta/ws/rs/core/Response.class)
class file has wrong version 55.0, should be 52.0
Please remove or make sure it appears in the correct subdirectory of the classpath.
[INFO] 1 error

You will have to exclude the resource test from the Java 8 run .... look in the .github/workflows/actions.yml for how it has been done for other API tests for Java 8 only

[apeiris]

Close #385 and resubmit without running this specific test