feat: add AWS/AppRunner as supported service

[fabiiw05]

I have confirmed that it can be retrieved using the following configuration.

apiVersion: v1alpha1
discovery:
  jobs:
  - regions:
    - us-east-1
    period: 300
    length: 300
    type: AWS/AppRunner
    metrics:
      - name: MemoryUtilization
        statistics: [Average, Maximum]
      - name: CPUUtilization
        statistics: [Average, Maximum]
      - name: 2xxStatusResponses
        statistics: [Sum]
      - name: Requests
        statistics: [Sum]
      - name: RequestLatency
        statistics: [Average]
      - name: ActiveInstances
        statistics: [Maximum]
      - name: 4xxStatusResponses
        statistics: [Sum]
      - name: Concurrency
        statistics: [Maximum]