Issue

When envFrom includes a prefix setting, the scale resolver ignores this prefix and adds environment variable keys to the ScalerConfig without the prefix.

apiVersion: v1
kind: ConfigMap
metadata:
  name: kafka-config
data:
  BOOTSTRAP_SERVERS: "kafka.example.com"
  PORT: "9092"
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: dummy-app
  labels:
    app: dummy-app
spec:
  selector:
    matchLabels:
      app: dummy-app
  template:
    metadata:
      labels:
        app: dummy-app
    spec:
      containers:
      - name: app-container
        image: nginx:latest
        envFrom:
        - configMapRef:
            name: kafka-config
          prefix: "KAFKA_" # Having PREFIX

resolveEnv is ignoring the prefix setting and loading envs without prefix:
Actual:

BOOTSTRAP_SERVERS
PORT

Desired:

KAFKA_BOOTSTRAP_SERVERS
KAFKA_PORT

Provide a description of what has been changed.

FIX

resolveEnv correctly applies prefixes to keys when a prefix is specified.

1. Get prefix, prefix is an empty string if not set
2. Prefix Env Key : prefix + k

Checklist

• When introducing a new scaler, I agree with the scaling governance policy
• I have verified that my change is according to the deprecations & breaking changes policy
• Tests have been added
• Changelog has been updated and is aligned with our changelog requirements
• A PR is opened to update our Helm chart (repo) (if applicable, ie. when deployment manifests are modified)
• A PR is opened to update the documentation on (repo) (if applicable)
• Commits are signed with Developer Certificate of Origin (DCO - learn more)

Fixes #6728