* feat(router.py): initial commit for loadbalancing azure batch api endpoints
Closes https://github.com/BerriAI/litellm/issues/5396
* fix(router.py): working `router.acreate_file()`
* feat(router.py): working router.acreate_batch endpoint
* feat(router.py): expose router.aretrieve_batch function
Make it easy for user to retrieve the batch information
* feat(router.py): support 'router.alist_batches' endpoint
Adds support for getting all batches across all endpoints
* feat(router.py): working loadbalancing on `/v1/files`
* feat(proxy_server.py): working loadbalancing on `/v1/batches`
* feat(proxy_server.py): working loadbalancing on Retrieve + List batch
