replace external redmine-java-api with internal implementation

[Pilopa]

Proposed changes

Replaces the external redmine rest api java dependency with an internal implementation due to irresolvable bugs in the dependency.

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• [x] PR is well described
• [x] Related issues linked to PR if existing and labels set
• [x] Target branch is not master (in most cases develop should bet the target of choice)
• [x] Code does not conflict with target branch
• [x] New code is covered with unit tests
• [x] CHANGELOG.md updated
• [ ] Definition of Done's fulfilled: DoD // UI DoD
• [ ] Documentation updated (only necessary for new features or changed behaviour)

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• [ ] Branch is green/blue on Jenkins
• [ ] Quality Gate passed on SonarQube

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities (and 0 Security Hotspots to review)
0 Code Smells

80.4% Coverage
0.0% Duplication