[PB-5727]: upload concurrently with worker pool to improve speed

[AlexisMora]

What is Changed / Added

now, create and update flows now run 10 uploads concurrently via async.queue,
also.introduced executeAsyncQueue(items, executor, config) as a generic wrapper. Both createBackupUploadExecutor and createBackupUpdateExecutor implement the same TaskExecutor interface and plug directly into it.
uploads now retry up to 3 times with [1s, 2s, 4s] exponential backoff before giving up on a file
The logic per file is identical to the old implementation:

Upload bytes to bucket -> get contentsId
Create/override metadata in backend
On metadata failure -> clean up uploaded content (create only; update matches old behavior of not cleaning up)
FILE_ALREADY_EXISTS -> skip silently
Non-fatal errors ->tracked in backupErrorsTracker
Fatal errors -> stop all uploads immediately
The only intentional behavior changes are: concurrency (10 parallel instead of 1) and retry (3 attempts with backoff instead of 0).

[sonarqubecloud]

Quality Gate failed

Failed conditions
66.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud