Streaming conversion mode

[vruusmann]

The JPMML-Converter library is currently stuck in the " file in -> PMML file out" mindset. End users keep asking for more output options, such as URL or plain streaming:
https://stackoverflow.com/questions/74656521/how-to-save-xgboost-lightgbm-model-to-postgresql-database-in-python-for-subseque/74659868#comment131843709_74659868

Conceptually, JPMML converter command-line applications could support UNIX-style piping, which may make integration with non-Java application environments easier:

$ java -jar pmml-converter-executable-${version} < input.file > output.file