add keycloak themes

keycloak-templates/themes/README.md

keycloak-templates/themes/ozg-by/login/footer-links.ftl

keycloak-templates/themes/ozg-by/login/theme.properties

keycloak-templates/themes/ozg-sh/login/footer-links.ftl

keycloak-templates/themes/ozg-sh/login/theme.properties

keycloak-templates/themes/ozg/login/footer-links.ftl

keycloak-templates/themes/ozg/login/resources/css/styles.css

...mplates/themes/ozg/login/resources/img/OZG_Cloud_Logo.png

keycloak-templates/themes/ozg/login/template.ftl

keycloak-templates/themes/ozg/login/theme.properties