use gha to build image-tools container (#6)

we haven't been auto-building the image tools container for quite some time now
this adds automation to build+push the container, but will only set `latest` if a new tag is pushed.

.github/workflows/site_tools.yml

@@ -0,0 +1,46 @@
+name: build image tools container
+
+on:
+  push:
+    branches:
+      - "master"
+    tags:
+      - "v*"
+  pull_request:
+    branches:
+      - "master"
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Docker metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ghcr.io/chameleoncloud/chameleon_image_tools
+          tags: |
+            type=ref,event=branch
+            type=ref,event=tag
+            type=ref,event=pr
+            type=sha
+
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}