Replace Java ExtractorCLI with equivalent C# service

[rkm]

The purpose of the ExtractorCLI tool is to kick-start an extraction request by reading a CSV file and some CLI arguments, and sending a few RabbitMQ messages.

Currently this is implemented in Java which, although it is functional, has a few maintainability issues:

• Duplication of message classes between C#/Java which require to be updated in sync
• Requires a separate application to be deployed instead of being bundled in the single smi script
• Our developers are less familiar with the Java ecosystem, and so that part of the repo is more susceptible to bit-rot

I don't see any strong reason why we shouldn't replace the Java service with an equivalent C# implementation