[JIRAALIGN-2777] API 2.0: All Program IDs can be removed from a Solution Objective

Issue Summary

Using the API, all Program IDs can be removed from a Solution Objective. This is inconsistent with the UI (at least one Program ID is required) and causes Solution level OKR reports to not show.

Steps to Reproduce

1. Create a Solution objective through the UI. 
2. Notice the Program field is auto-populated with all programs under the Solution.
3. Attempt to remove all Programs and notice the modal not allowing you to save the Solution objective with no programs.
4. Create a Solution objective through the API. 
5. Use get call to view the Objective JSON and notice all of the program Ids.
6. Use a put or patch to remove all program Ids.

Expected Results

The API should not allow you to remove all program Ids on a Solution objective (validation should exist requiring at least one).

Actual Results

The API should not allow you to remove all program Ids on a Solution objective. When this occurs, solution level Objective reports are not accessible.

Workaround

Do not remove all Program IDs on a Solution ID (there always needs to be at least one).