fix: Ensure multi-platform builds with Docker Buildx

This commit updates the GitHub Actions workflows to correctly set up
Docker Buildx for multi-platform (amd64, arm64) image builds.

Previously, the workflows were missing the `docker/setup-buildx-action`
step, which led to errors when attempting multi-platform builds as the
default Docker driver does not support this.

The following changes were made:
1.  **Added `docker/setup-buildx-action@v3`:**
    - This step is now included in both the CI (`.github/workflows/ci.yaml`) and Release (`.github/workflows/release.yml`) workflows before the QEMU setup and build/push actions.

2.  **Dockerfile (`exporter/Dockerfile`):**
    - Remains as per the previous commit, using `TARGETARCH` to correctly copy architecture-specific libraries. This part was already correct for multi-arch builds.

3.  **Helm Chart:**
    - No changes were required for the Helm chart.

This ensures that the CI/CD pipeline can successfully build and push
Docker images for both `linux/amd64` and `linux/arm64` architectures.

.github/workflows/ci.yaml

@@ -31,6 +31,9 @@ jobs:
       - name: Check out code
         uses: actions/checkout@v3
 
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v2
 

.github/workflows/release.yml

@@ -36,6 +36,9 @@ jobs:
       - name: Check out code
         uses: actions/checkout@v3
 
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v2