Refactor ORCA so that it could support extensible storage

Currently, Postgres `Access Method` is not supported by ORCA, since storage type is hard coded.
We need to refactor ORCA so that it could support more storage type, for example, Hash Index, and etc

Start by locating ORCA's hard-coded storage-type handling and reading how PostgreSQL Access Methods are represented. The issue names no files, entry points, or tests, so first map the affected storage logic and determine the design needed for extensibility. Done should include support for additional storage types such as hash indexes.

Written by the indexing model from the issue text.