I'll try to do a fuller review before I head into vacation from Tuesday afternoon – but in case I don't get to, and you request review from someone else, just want to leave an initial thought here:

I would suggest that instead of naming this command sentry-cli upload-dart-symbol-map, we name it sentry-cli dart-symbol-map upload.

The reason is that this aligns with the APIs for debug-files upload and sourcemaps upload. Also, this would then mean we have a dart-symbol-map subcommand, with an upload command nested below. That way, if we ever want to add more functionality related to Dart symbol maps, we can also add this functionality under the dart-symbol-map subcommand.

Thanks, will update the command

thx, yes works as expected