feat: include commit has in image tag (#2)

Co-authored-by: Timo Behrendt <t.behrendt@t00n.de>
Reviewed-on: #2

.drone.yaml

@@ -7,7 +7,9 @@ steps:
   - name: build
     image: docker:20
     commands:
-      - docker build -t gitea.t000-n.de/t.behrendt/backupsidecar:latest .
+      - COMMIT_HASH=$(git rev-parse --short HEAD)
+      - IMAGE_TAG=gitea.t000-n.de/t.behrendt/backupsidecar:$COMMIT_HASH
+      - docker build -t $IMAGE_TAG .
     when:
       event:
         - push
@@ -22,7 +24,9 @@ steps:
       password:
         from_secret: REGISTRY_PASSWORD
       repo: gitea.t000-n.de/t.behrendt/backupsidecar
-      tags: latest
+      tags: 
+        - latest
+        - $COMMIT_HASH
     when:
       event:
         - push