Add support for blocking/non-blocking syncs

[varmar05]

With upcoming change on server which would allow 1 blocking and N unblocking uploads we need to split work by changes/file type to benefit from uploads concurrency.

Group pending (push) changes into separate uploads:

• non-blocking with only added non-versioned and not qgis project data (e.g. all but .gpkg, .qgs, qgz)
• blocking one with the rest of changes (incl. updated/removed files)

Then client can start sending chunks via multiple upload transactions to improve overall performance.

Because every push finish request will bump project version it might happen that 2 concurrent finish request could collide (race conditions). In such scenario server would temporarily block 2nd request with 409 error code and client just need to wait and retry finish.

[varmar05]

Let's start with some simple strategy by splitting local changes by type and send first blocking upload and when finished continue with non-blocking (which would other users eventually create their blocking transactions).