Introduce whitelist proxy microservice

[ahennr]

Description

This PR introduces a HTTP whitelist proxy microservice which is basically the migration of the existing one of shogun-core.
The white-listed hosts can be added in the list proxy.whitelist in application.yml.

Plz review @terrestris/devs

Related issues or pull requests

Pull request type

• Bugfix
• Feature
• Dependency updates
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe)

Do you introduce a breaking change?

• Yes
• No

Checklist

• I understand and agree that the changes in this PR will be licensed under the
  Apache Licence Version 2.0.
• I have followed the guidelines for contributing.
• The proposed change fits to the content of the code of conduct.
• I have added or updated tests and documentation, and the test suite passes (run mvn test locally).
• I have added a screenshot/screencast to illustrate the visual output of my update.

[dnlkoch]

Is the OpenAPI UI included in the MS?

[ahennr]

Is the OpenAPI UI included in the MS?

Not yet. Since no entities / REST / graphql endpoints end have been added here, I didn't see the need for this. However, I'll add this if wanted.

[dnlkoch]

No, I don't see any benefit neither - was just wondering.

[ahennr]

thx for reviews