fix: Use python:3.13-alpine for metrics-exporter (GoogleCloudPlatform#1520)

Author: NimJay

cost-optimization/gke-vpa-recommendations/metrics-exporter/Dockerfile

@@ -1,7 +1,6 @@
-
-FROM python:3.13 
+FROM python:3.13-alpine
 WORKDIR /app
 COPY requirements.txt requirements.txt
 RUN pip install -r requirements.txt
 COPY . .
-CMD ["python", "./main.py"] 
+CMD ["python", "./main.py"]