Workspaces changes the way to test APIs with a subscription key

[ferantoMSFT]

Describe the bug After creating a new APIM instance and testing the Echo API, subscription keys cannot be fetched automatically now.

To Reproduce Steps to reproduce the behavior:

1. Deploy new API Management instance
2. Go to 'APIs'
3. Click on 'Echo API'
4. Click on 'Test' tab
5. See error

Expected behavior We should be able to document how to easily test the Echo API.

Screenshots