BlobStore uncompress argument should be Boolean

The doc says we can pass the config when launching a topology with

topology.blobstore.map='{"key1":{"localname":"blob_file", "uncompress":"false"},"key2":{}}'

However, it will trigger ObjectReader.getBoolean() function and then throw an IllegalArgumentException.

We need to update the doc for "uncompress" argument from String (e.g. "false") to Boolean (e.g. false)