[serve] Transform replica level metrics to AutoScalingContext constructor args

[snorkelopstesting2-coder]

Recreated from original PR: ray-project/ray#57202

Changes

1. Wire up the AutoScalingContext constructor args to make metrics readable in the custom AutoScalingPolicy function.
2. dropped requests_per_replica since its expensive to compute
3. renamed queued_requests to total_queued_requests for consistency with total_num_requests
4. added total_running_requests
5. added tests assert new fields are populated correctly
6. run custom metrics tests with RAY_SERVE_AGGREGATE_METRICS_AT_CONTROLLER = 0 and 1
7. updated docs