Migrate to httpclient5

[strangelookingnerd]

Replaces outdated httpclient4 with the successor httpclient5.

Testing done

mvn clean verify

Submitter checklist

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• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
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• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue