Switch nightly build to GH action (#290)

* Switch nightly build to GH action

Run a GitHub action job everytime a change is merged, instead of using centos-ci.

See eclipse/che#18072

Signed-off-by: Eric Williams <ericwill@redhat.com>

* Update secret name

Signed-off-by: Eric Williams <ericwill@redhat.com>

* Make action names more clear

Signed-off-by: Eric Williams <ericwill@redhat.com>

* Abstract centos-ci only steps

Only use provided scripts for:
* base image build + push
* happy path image build + push

Signed-off-by: Eric Williams <ericwill@redhat.com>