Request: Improved Exception Handling

[dehall]

There are a few ways the Validation Service can throw, and digging into the root cause of the problem is challenging:

• The full stack trace is not reported in the log
• Errors are not caught, which results in a blank response and nothing in the log. Not catching Error is usually best practice, but the core validator can throw Error in situations I think should be Exceptions, for example a profile URL that doesn't resolve. See sample request that throws an Error at the bottom of this message.
• The exception message is returned in the response body as just a string

I would propose the following, which I'm happy to implement but wanted a sanity check before submitting an unsolicited PR:

1. Log the full stack trace of the exception caught in this block instead of just the localized message

   org.hl7.fhir.validator-wrapper/src/jvmMain/kotlin/controller/validation/ValidationModule.kt

   Lines 42 to 46 in 7285a3f

   	try {
   	call.respond(HttpStatusCode.OK, validationController.validateRequest(request))
   	} catch (e: Exception) {
   	logger.error(e.localizedMessage)
   	call.respond(HttpStatusCode.InternalServerError, e.localizedMessage)

2. Change the catch to Throwable so that it will catch Error as well (then maybe re-throw Errors after responding?)
3. Wrap the exception in a ValidationResponse with level FATAL, that way the response structure is the same regardless of success or error. The HTTP status code would still indicate server error, bad request, or ok as appropriate.

Sample request that throws Error internally and results in a blank response body:

{
    "cliContext": {
        "sv": "4.0.1",
        "profiles": ["http:https://hl7.org/fhir/us/core/StructureDefinition/us-core-doesntexist"]
    },
    "filesToValidate": [
        {
            "fileName": "manually_entered_file.json",
            "fileContent": "{\"resourceType\":\"Patient\"}",
            "fileType": null
        }
    ]
}