Fix Configure JSON defaults sample

[apalm]

The Configure JSON defaults sample in the playground is currently broken. Validation errors never show up even when the JSON doesn't conform to the schema.

Here's what I had to change to get it to work:

• Set validate to true in diagnostic options.
• Create a model; for each schema, set fileMatch to a value that matches the uri used when creating the model. Reference: Set schema of JSON content without $schema property #191 (comment)

I also changed the initial JSON so that the validation errors show up without editing the JSON.

Test Plan

Ran gulp simpleserver. The validation errors now show up as expected.

[msftclas]

All CLA requirements met.

[alexdima]

Thank you! 👍