Define DP Release Schema

[raprasad]

• For @eedeleon
• Iterate w/ others in the community
• related to #39
• How does this differ from the current output of WN releases?

[raprasad]

• Feb version from @saniavn is here: https://github.com/privacytoolsproject/PSI-Library/blob/develop/dp-schema.json
  • https://github.com/privacytoolsproject/PSI-Library/blob/develop/schemadp-example.json

[saniavn]

@raprasad Please update the description for "rho" on line 195, nodeId on line 255, and constraints on line 260.

[raprasad]

• moved schema and example file to: https://github.com/opendifferentialprivacy/OpenDP-Experimental/tree/master/release_schemas