Cannot automatically trigger elk-live build when eclipse/elk-models changes

[Max Kasperowski]

In an ideal world we would like to automatically build a new elk-live image when elk-models is updated so that the examples are updated in elk-live as well.

These two PRs demonstrate how this could be done:
#83
eclipse/elk-models#21
also see this discussion

but it would require creating a secret in the elk-models repo, which we cannot do.

So for now the elk-live build must be manually triggered or we could also have it build nightly.