FDC3 Workbench intent raising control could be more intuitive

## Minor Issue
Please use minor issues for discrepancies or errors found in the spec or supporting documentation, examples, and other materials. If you wish to propose a new feature or a revision to an existing feature, please use the *Enhancement Request* template.

### Area of Issue
- [ ] App Directory
- [ ] API
- [ ] Context Data
- [ ] Intents
- [ ] Desktop Agent Bridging
- [ ] Use Cases
- [x] Other

### Issue Description:
When using the FDC3 workbench to test raising an intent I do not seem to be able to raise an intent. If I select an intent and click the "Raise Intent" button I get a validation error saying "Please Select a Context First":


It should be possible to raise an intent without a conext so IMHO this is an error but when I try to select a context I am unable to select an intent:


I am able to type in an intent and add that. Once I have done that I am able to raise an intent (this always fails but I suspect this is beacuse there are no listeners).

Start in the FDC3 Workbench by reproducing the reported flow: select an intent, click “Raise Intent,” and compare it with adding an intent manually. Trace the validation behind “Please Select a Context First” and the intent/context selection controls. Done means the documented intent-raising flow handles the context requirement consistently and its behavior is covered by the relevant Workbench test, if one exists.

Written by the indexing model from the issue text.