Spring boot integration test upgrade

[JonasKunz]

What does this PR do?

Part of #2942.

• Adds integration test for spring boot 3
• Adjusted the RestTemplate test-strategy: The project was upgraded to spring 6 and the integration test is used to test with older versions. This should make it easier to manage upgrades via dependabot.

Checklist

• This is something else
  • I have updated CHANGELOG.asciidoc

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• Start Time: 2023-05-11T10:39:15.465+0000

• Duration: 15 min 33 sec

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[github-actions]

/test

[jabrena]

I miss in the integration tests for Spring Boot 3, at least a test using Webclient, right?

[SylvainJuge]

LGTM, let's merge it.