Add ability to have services declare itself as tech-preview or mandatory

When a service is added to a stack, it should be identified as:
default/regular - service is optional on the cluster, UI usually shows it as
tech-preview - service may be deployed, UI will not auto-select these services and mark them as TechPreview
mandatory - service need to be deployed and all deployment should fail is the service is not selected during deployment
Lets create a proposal of what changes are needed in the services' metainfo.xml? Note that a service can change its attribute between stack versions - e.g. move from "tech-preview" to "mandatory".