knife data bag show should have a -f flag to write an item to a json file

As a sysadmin, I want to retrieve the data bag items from my chef server and store them in JSON because I might have forgotten to put them in source control first.

• I'm using the chef-repo with a data_bags directory.
• I want the bag directory to be auto-created
• I want the item to go into a json file in the directory for the bag it is in.

For example,

knife data bag show apps my_app -f data_bags/apps/my_app.json

Would end up creating:

data_bags/apps/my_app.json

Additionally, I would like to not have to remember the path to put the data bag and have knife automatically put the file in the right directory.

knife data bag show apps my_app -f my_app.json

Creates the data_bags/apps/my_app.json by default.