Fix/producer impl

[MinetteMeyo]

• Refactored AbstractProducer and all related classes, i.e., base producers, to clean unused code and remove redundant methods.
• Renamed all the concrete producers with their base producers' prefix. E.g., BTUProducer became CSVBTUProducer, and the same for tests and associated queries
• Fixed the issue with the absolute path in the repo. Two routes were defined in the application.properties file, and the ' AbstractProducer ' method was updated accordingly.
• Created a complete pipeline of to access TXT files from the hub in the middleware. All the queries rely on POST {baseurl}/apply/sync or async. All TXT files will rely on the TXTProducer; only the path (actually the filename) will differ