log all data loading errors

[fm3]

Bucket requests always return 200, if something went wrong during loading, the array is all-black and the MISSING-BUCKETS header is set. However, no error information is contained.

There is already good error logging in BinaryDataService.handleBucketRequest for everything that happens inside of BucketProvider.load.

However, if the errors occur after that, e.g. while applying the agglomerate mapping, nothing is shown. This error logging should be moved to handleDataRequests or another type of error logging should be created at that level there. Maybe include the errors in the response headers? (Or is that too verbose/can sensitive information be leaked?)

[frcroth]

Log errors in "convertIfNecessary" (might need to give request as argument for more info in log). Use rate limiting with datasetErrorLoggingService? -> Code dup