Image names must be lower-cased in order for skaffold to work

We just ran into a problem where the image name in skaffold and values.yaml was like this:

```
ghcr.io/Raffy23/sturdy-barnacle
```

This didn't work, and we had to make it lowercase:
```
ghcr.io/raffy23/sturdy-barnacle
```

FYI @Raffy23 

Files affected: https://github.com/keptn-sandbox/keptn-service-template-go/blob/master/.github/workflows/initrepo.yml
