ci(charts): Rename chart build jobs

This patch is a workaround for gitlab jobs that merge themselves by
accident. it should be further refined, similar to the images setup to
have a more generalised pipeline in the future.

charts/keycloak/.gitlab-ci.yaml

-build:
+chart-build-keycloak:
   stage: build
   image: quay.io/helmpack/chart-testing:v3.6.0
   script:

charts/mok/.gitlab-ci.yaml

-build:
+chart-build-mok:
   stage: build
   image: quay.io/helmpack/chart-testing:v3.6.0
   script: