Migrate to httpclient5

[strangelookingnerd]

Replaces outdated httpclient4 with the successor httpclient5.

Testing done

mvn clean verify

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[jonesbusy]

@strangelookingnerd Thanks! Were you able to perform some interactive tests?

I'm afraid this plugin lack of integration tests and missing coverage

If not I will try to perform quick tests soon

[strangelookingnerd]

I set up a simple job with FileDownloadOperation to download something from a simple webserver. It did not crash so I was satisfied, however there was no authentication or redirects involved.