Handle errors that cause image to be stuck in processing

[xaneem]

When the backend code picks up an image, we set the status to "processing" in the queue. But if the code fails in any case, it's not handled and it remains in "processing" state.

A better approach would be:

• Allot a time for processing to happen; if it doesn't get processed within that time, set it to retry or mark it as "failed"
• If retry is configured, set a maximum number of retries before it gets marked as failed.

This is straightforward to do, and can be done with changes in the worker.js script alone.

[xaneem]

4c5cb627f1cf31c052a6738c6f96044542ef3b48 removes failed items from queue

ed829ff92f6f1fb1528a01e763c7a69d14b1b61c removes items stuck in processing

Retry logic is good to have, but not implemented.