[CDCSDK] Handle DDL on enum and composite type

[arpang]

Jira Link: DB-3439

Description

We support enum and composite types in CDC.

A DDL on these types renders the cache stale. This is a current limitation as we do not handle DDL operations on these types in CDC. The task is to handle this.

Whenever we encounter a DDL entry on a UDT types (enum or composite), we can fetch fresh metadata from the master for this type. In the RPC GetUDTypeMetadataRequestPB, an optional field pg_type_oid is added for this purpose.

Internal reference: https://docs.google.com/document/d/1MzHV2ijweI1WMQNRu0A7er93Ff8n0zVNMKE_rpHI5L8/edit#