Ask for API version when user associates pull request

**Requirement:** SDK stakeholders have asked for the API Spec version data. There is not a way to programmatically determine and validate the API version. Update the API readiness milestone to ask the user to enter the API version and update the API Spec work item field `API Spec version` with the input by the user.

**Proposed UI changes:**

Also in the Release Planner app update the UI with:
API details - Add new field named "API version" with the value of the API version as indicated by the user.