CsvTarget to enable processing of completed lines of csv files in chunks

[gabrielcedran]

The CsvTarget enables developers to load csv files in chunks, process the lines applying their own logic as they are completed by the chunks (e.g saving the lines into a db, send to another api, save into a file, etc) and remove them from the memory to prevent memory overflow.

In our project, our use case consisted of processing huge csv files where business logic needed to be applied for each line and then eventually they should be converted into domain objects and saved into a database.

Adapted example of our use case in flask:

`

def post(self):
    parser = StreamingFormDataParser(headers=request.headers)
    
    file_ = CsvTarget()
    parser.register('file', file_)

    while True:
        chunk = request.stream.read(1024)
        if not chunk:
            break
        parser.data_received(chunk)
        completed_lines = file_.pop_lines() # memory freed for the next iteration
        process_entries(completed_lines)

    completed_lines = file_.pop_lines(include_partial_line=True) # not necessarily a csv file ends with a linebreak
    process_entries(completed_lines)
    return {"message": "CSV uploaded successfully"}, 200

`

[siddhantgoel]

Thanks for the PR! I left some minor comments but overall it looks good.

[siddhantgoel]

Thanks for the PR! I just published v1.14.0 which includes this.