Release builds need to fail if a git tag already exists

It is possible when doing a release that we overwrite an existing release by re-pushing an image. 

To avoid this the release pipeline should fail if a git tag already exists. 

```
if git rev-parse "$VERSION" >/dev/null 2>&1; then	
    echo "Tag $VERSION already exists. Doing nothing."	
    exit 1	
fi
```