DOT-6786: Add support for concurrent snapshot upload in case of remote discovery

[lt-zeeshan]

This pull request introduces support for configurable concurrent snapshot processing in the queue system. The main changes include adding a new MAX_CONCURRENT_PROCESSING environment variable, updating the Env type, and refactoring the snapshot queue logic to process multiple snapshots in parallel based on this configuration.

Configurable concurrency for snapshot processing:

• Added a new environment variable MAX_CONCURRENT_PROCESSING to control the maximum number of snapshots processed in parallel, with parsing and defaulting logic in src/lib/env.ts and the Env type updated in src/types.ts. [1] [2] [3]
• Introduced MAX_CONCURRENT_PROCESSING and activeProcessingCount properties in the Queue class (src/lib/snapshotQueue.ts) to manage and track concurrent processing.

Queue processing logic improvements:

• Refactored the processNext method in Queue to batch and process multiple snapshots concurrently when remote discovery is enabled and certain config flags are set, using the new concurrency controls.
• Added a new processSnapshot method to encapsulate single snapshot processing, and updated flow to avoid recursive calls and ensure proper concurrency management. [1] [2] [3]