CTS213 — Using enumerations instead of using code systems

The PIM uses enumeration rather than having a code system of its own. This does not allow for new codes to be added easily (need another enumeration), a separate documentation is needed for the definition of what the enumerations mean, and translations are not possible. Two such examples are the enumeration Resource Type with 7 possible values such as CODE_SYSTEM, CODE_SYSTEM_VERSION, CONCEPT_DOMAIN, MAP, MAP_VERSION, VALUE_SET, VALUE_SET_DEFINITION and the enumeration CHANGE TYPE with the enumerations: CREATE, UPDATE, METADATA, DELETE, CLONE, IMPORT. It would good terminology practice for the international specifications of terminology server to use an internal code system rather than use enumerations. Logged: https://github.com/cts2/cts2-specification/issues/145