Really, only .json file? I am not sure if we are on same page because I have many experiences injecting .csv files into Elastcisearch to create an index by running Logstash config file. You could verify my project from my github account.(https://github.com/sampanayak/ccfl-elastic.git).
Also regarding uploading .csv file please check the screen shot attached with this message, where I was able to upload the file and create an index pattern for that.
