[Reporting] Classify user errors correctly

[tsullivan]

If a report job fails, the failure is marked as an "unsuccessful" task outcome by Task Manager metrics. However, there are certain cases where a failure can be due to user configuration and would be expected:

1. If the report job depends on a saved object, and that saved object is deleted before the report task runs
2. If the authentication that is cached in the report job document becomes invalid before the report task runs.

This issue is to update Reporting code to account for these kinds of cases when handling errors, so that task outcomes metrics aren't affected.

An example of how this is done elsewhere is here (note throw createTaskRunError(err, TaskErrorSource.USER);).

[elasticmachine]

Pinging @elastic/appex-sharedux (Team:SharedUX)

[tsullivan]

If the report job depends on a saved object, and that saved object is deleted before the report task runs

More context:

This type of error can be caught for CSV exports. When generate_csv.ts calls searchSourceStart.create, there is chance the call could fail if the stored index pattern for the search has been deleted. The requirements should be to:

1. Wrap the error in a type of ReportingError, so we can have an error code which can map to a user-friendly error message that users will see in Stack Management > Reporting. Doing this work is tracked here: [Reporting] Handle error scenarios for deleted user and deleted saved object #191548 (comment)
2. Pass that error to createTaskRunError

A overly-simplified solution would look something like:

let searchSource;
try {
  searchSource = await this.dependencies.searchSourceStart.create(this.job.searchSource);
} catch (error) {
 if (error.code === '404') { // Have to find a valid way to identify the nature of the error
   const reportingError = new ReportingSavedObjectNotFoundError(error); // Have to define and export this error class in packages/kbn-reporting/common/errors.ts
   throw createTaskRunError(reportingError, TaskErrorSource.USER);
 }
}