Limit for simultaneous uploads

[PVince81]

In OC 10 we only ever upload a single file, no parallelism.

In Phoenix the upload is running in parallel.

To avoid overloading the network queue, we should add a limit to the number of parallel requests.
I wonder if we should just make it one, at least for now.

@DeepDiver1975

[PVince81]

Also need to check for other operations like deleting files, trashbin, etc

We need a generic mechanism for such operations.

[PVince81]

This is needed also to avoid blocking important requests like token refresh requests.

[PVince81]

As discussed internally, let's make it one for now. A simple queue should be enough.

We can look into more clever parallelization later on. I'd see chunking has higher priority (even sequential) before parallelization.

[PVince81]

As far as I can see we already have a p-queue (promise queue) in place for directory uploads, but it isn't used for regular uploads.

We should consolidate all those mechanisms.

Basically only have a single p-queue for all uploads, which can also be filled later on if the user adds more uploads while current uploads are running.

[PVince81]

correction, the p-queue is only used for creating folders that originate from a directory upload.

the upload of files there is still happening in parallel

[PVince81]

PR here: #2653