arg support for upload-schemas.js

[vuldin]

upload-schemas.js currently hard-codes the files it loads to get schema details as well as the subjects where those schemas are uploaded to in the registry. These could be turned into variables that are passed to the script either as CLI arguments or from a config file.

upload-schemas.js is for now found in a PR here: https://github.com/redpanda-data/redpanda-examples/pull/12/files#diff-79258c186dc107a6af28400e7248a0f64de14cc697c8fc95c596deefde666409