Organize the constants

[gary-lgy]

Currently constants are defined in a couple of places:

• pkg/controllers/common/constants.go
• controller's own package
• pkg/util packages

We should organize them so they are more maintainable. When organizing, we should make sure:

• the constants are exposed to all packages in the project and not just for pkg/controllers
• the constants are categorized properly
• unused constants should be removed