Prometheus metrics for ingest wal usage are not working

Describe the bug

Both quickwit_ingest_wal_disk_used_bytes and quickwit_ingest_wal_memory_used_bytes are not working as expected. quickwit_ingest_wal_disk_used_bytes displays a constant value of 134217728 (max queue disk usage is set to 32GB and total size of disk is 250G). quickwit_ingest_wal_memory_used_bytes always report 0.

Steps to reproduce (if applicable)
I'm using default Prometheus scraping configuration provided by the helm chart. These are my ingest_api values:

  ingest_api:
    max_queue_memory_usage: 4GiB
    max_queue_disk_usage: 32GiB

Expected behavior
I expect both metrics to report WAL usage for both disk and memory.

Would also be great to have metrics to show max_queue_disk_usage and max_queue_mem_usage config setting.

Configuration:
Version: v0.8.1

node.yaml:

data_dir: /quickwit/qwdata
default_index_root_uri: s3://prod-<redacted>-quickwit/indexes
gossip_listen_port: 7282
grpc:
  max_message_size: 80 MiB
indexer:
  enable_otlp_endpoint: true
ingest_api:
  max_queue_disk_usage: 32GiB
  max_queue_memory_usage: 4GiB
listen_address: 0.0.0.0
metastore:
  postgres:
    acquire_connection_timeout: 30s
    idle_connection_timeout: 1h
    max_connection_lifetime: 1d
    max_connections: 50
    min_connections: 10
storage:
  s3:
    region: us-east-1
version: 0.8

Start by tracing the quickwit_ingest_wal_disk_used_bytes and quickwit_ingest_wal_memory_used_bytes metrics through the ingest API and the default Helm Prometheus scraping configuration. Reproduce the reported values with max_queue_memory_usage set to 4GiB and max_queue_disk_usage set to 32GiB; done means both metrics reflect WAL disk and memory usage, with any added limit metrics matching the configured values.