Promtail /metrics in kubernetes

We are using promtail 2.8.4 in Kubernetes 1.24.
We want to define custom metrics in promtail.
We use config below but we do not see the metrics in prometheus.

promtail-values.yaml file is like:

config:
snippets:
pipelineStages:
- cri: {}
extraScrapeConfigs: |

  - job_name: shift-custom
    pipeline_stages:
      - regex:
          expression: '(?P<exception>.*Exception: .*)'
      - metrics:
          shift_custom_exceptions:
            type: Counter
            description: "Exceptions"
            source: exception
            config:
              action: inc
    kubernetes_sd_configs:
      - role: pod