feat(anubis): add /healthz route to metrics server

Also add health check test for Docker Compose and update documentation
for health checking Anubis with Docker Compose.

Signed-off-by: Xe Iaso <me@xeiaso.net>

.github/workflows/smoke-tests.yml

@@ -10,7 +10,13 @@ permissions:
   contents: read
 
 jobs:
-  git-clone:
+  smoke-test:
+    strategy:
+      matrix:
+        test:
+          - git-clone
+          - git-push
+          - healthcheck
     runs-on: ubuntu-24.04
     steps:
       - name: Checkout code
@@ -30,28 +36,5 @@ jobs:
 
       - name: Run test
         run: |
-          cd test/git-clone
-          ./test.sh
-
-  git-push:
-    runs-on: ubuntu-24.04
-    steps:
-      - name: Checkout code
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
-        with:
-          persist-credentials: false
-
-      - uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
-        with:
-          node-version: latest
-
-      - uses: actions/setup-go@d35c59abb061a4a6fb18e82ac0862c26744d6ab5 # v5.5.0
-        with:
-          go-version: stable
-
-      - uses: ko-build/setup-ko@d006021bd0c28d1ce33a07e7943d48b079944c8d # v0.9
-
-      - name: Run test
-        run: |
-          cd test/git-push
+          cd test/${{ matrix.test }}
           ./test.sh