Split upload_rr_trace to enable manual upload.

[maleadt]

Automatic uploading of the trace can sometimes fail, see e.g. JuliaGPU/CUDA.jl#2163 (comment). In this PR, I provide a fallback, where the user can still manually upload a trace if the upload was interrupted or canceled.

@Liozou I changed the errormonitor logic you added in #144; IIUC all errors should have been reported by errormonitor, so it should be safe to just return from the catch block.

[Liozou]

Sure, that also works! The control flow will be different though since errormonitor does not interrupt the computation, it only prints an error message if there is a problem (typically a network error) so what used to be rethrown will now simply print an error message and return nothing instead. I think it's fine.