Incorrect name for `detail` field in ErrorResponse

### Bug Description:

According to the TSP specification, the field for detail called `detail` instead of `details`. This needs to be corrected.

### Steps to Reproduce:

Use the error response detail in vscode-trace-extension:

You will see that it won't compile unless you call it `details`. However, `details` is not sent by a compliant trace server.

### Additional Information

- Operating System: Any
- Version: v0.9.0