[BUG] malformed env JSON gives "Error: Invalid env" message with no context

[tonybaloney]

I ran the GitHub action with the following input

- name: 'Azure Load Testing'
        uses: azure/load-testing
        with:
          loadTestConfigFile: 'loadtest/smoketest.yaml'
          loadTestResource: ${{ env.AZURE_LOAD_TEST_NAME }}
          resourceGroup: ${{ env.AZURE_RESOURCE_GROUP_NAME }}
          env: |
            [
              {
              "name": "domain",
              "value": ${{ env.AZURE_LOAD_TEST_HOST }}
              }
            ]

This returned Error: Invalid env.

env could refer to :

1. The environment variables
2. The workflow environment variables
3. The action environment variables
4. The env parameter

The actual issue was that the JSON in env parameter was invalid because it was missing quotes, but it was difficult to diagnose. Please can you update the error message here to be more specific https://github.com/Azure/load-testing/blob/main/src/mappers.ts#L388-L390

The exception object has a detailed message on why JSON.parse failed but this context is being lost