Add Icinga Kubernetes Web

This PR adds `Icinga Kubernetes Web` to the image. Note that there's no
release yet for `Icinga Kubernetes Web`. So for releases of the image,
we have to set `MODE` to `snapshot` right before the module gets cloned.
Also note that `MODE` is not reset, so be careful when adding code after
this change.

get-mods.sh

@@ -92,3 +92,6 @@ get_mod pdfexport
 get_mod reporting
 get_mod vspheredb
 get_mod x509
+# Icinga Kubernetes Web does not yet have a release, but should also be included.
+# Be careful when adding code after the following line, as MODE will not be reset.
+MODE=${MODE/release/snapshot} get_altname icinga-kubernetes-web kubernetes