fixup DicomAnonymiser CTP implementation

[rkm]

Proposed Changes

TODO:

• Download ctp-anon-cli for integration testing
• Figure out error handling when CTP subprocess goes away (e.g. killed, OOM)

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that would cause existing functionality to not work as expected)
• Documentation-Only Update (if none of the other choices apply)
  • In this case, ensure that the message of the head commit from the source branch is prefixed with [skip ci]

Checklist

By opening this PR, I confirm that I have:

• Reviewed the contributing guidelines for this repository
• Ensured that the PR branch is in sync with the target branch (i.e. it is automatically merge-able)
• Updated any relevant API documentation
• Created or updated any tests if relevant
• Created a news file
  • NOTE: This must include any changes to any of the following files: default.yaml, any of the RabbitMQ server configurations, GlobalOptions.cs
• Listed myself in the CONTRIBUTORS file 🚀
• Requested a review by the @SMI/Reviewers team

Issues

[rkm]

CC @jas88 feel free to pick this up if you have time