Minimize required configs to work out of the box

Provide optimized default values when a field in config file is missing,
so it's easier for inexperienced users to try and experiment with this project.

For example:
If the `rss.storage.type` field is missing , it may defaults to `MEMORY_LOCALFILE_HDFS`.
Currently, it throws `NullPointerException: Name is null`.

In summary, let's try make the default settings work out of the box.
Please refer to how easy it is to setup a single node cluster for HDFS or Spark.

No source file or test is named. Start by locating configuration handling for rss.storage.type and compare it with the single-node HDFS or Spark setup; done means missing fields resolve to usable defaults and no longer produce the reported NullPointerException.

Written by the indexing model from the issue text.