Implement Default Forums Object

[rootelement]

When a challenge is saved as draft, please add these properties to the challenge object for a challenge type or f2f type to trigger a forum create. We can then work to make this configurable, including track/type ids that have this enabled by default, how tasks don't create forums, etc.

This is just the first step.

Example object:

"challenge.discussions": [
  {
    "name": "My Forum Name",
    "type": "challenge",
    "provider": "vanilla"
  }
]

Reference challenge api issue:
topcoder-platform/challenge-api#290 (comment)

NOTE
The challenge API will not accept this object until this PR is merged into develop. I'm estimating daytime Weds Sept 30th EDT.
topcoder-platform/challenge-api#309

[rootelement]

@vikasrohit i assigned this to you for now, it's up to you if you want to task this out and get a PR pending for dev so we can add this at the same time.

[maxceem]

@vikasrohit this is done via PR #846. This PR can be already merged if you like because API doesn't complain about submitting discussions property even now.

The forum name is formatted as ${challenge.name} Discussion, but let me know if it should be different.