Export librelink values as Prometheus metrics

Thank's for a great project.

The PR is not meant to be merged, due to modified github workflow. Filed in case anyone else is looking for Freestyle Libre to Prometheus. There's docker images at https://github.com/users/solsson/packages/container/package/nightscout-librelink-up. I could also make a code-only PR if someone is interested in a merge.

Running this in Kubernetes with the following yaml

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: librelink-exporter
  labels:
    app: librelink-exporter
spec:
  replicas: 1
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 0
      maxUnavailable: 1
  selector:
    matchLabels:
      app: librelink-exporter
  template:
    metadata:
      labels:
        app: librelink-exporter
    spec:
      containers:
      - name: app
        image: ghcr.io/solsson/nightscout-librelink-up
        env:
        # kubectl create secret generic librelink-auth --from-literal=username= --from-literal=password=
        - name: LINK_UP_USERNAME
          valueFrom:
            secretKeyRef:
              name: librelink-auth
              key: username
        - name: LINK_UP_PASSWORD
          valueFrom:
            secretKeyRef:
              name: librelink-auth
              key: password
        - name: LINK_UP_TIME_INTERVAL
          value: "1"
        ports:
        - containerPort: 8080
          name: http
---
apiVersion: monitoring.coreos.com/v1
kind: PodMonitor
metadata:
  name: librelink-exporter
  labels:
    [your prometheus matcher]
spec:
  jobLabel: app
  namespaceSelector:
    any: false
  selector:
    matchLabels:
      app: librelink-exporter
  podMetricsEndpoints:
  - port: http
    path: /metrics

timoschlueter / nightscout-librelink-up

Export librelink values as Prometheus metrics #89