Add pre and post flatten validations for devfile

• Separate our validations as pre-flatten and post-flatten
• Moved parent validation to pre-flatten. This is required because the parent gets resolved during flattening. Although we have fixed parent flattening issue in the devfile gem, we are choosing to restrict it on monolith side because there are security implications. A parent can be referenced by a registryUrl or a uri which can have any arbitrary URL which is a security threat.
• Add validation for dedicatedPod, projects, starterProjects, event types

This feature is behind a feature flag. The rollout issue can be viewed at Add pre and post flatten validations for devfile (!119865 - merged) .