[Improvement] Catalog document should be improved.

### What would you like to be improved?

Catalog is very critical part of service for Gravitino, and we should have a well organized documentation, such as Hierarchical one as: RESTful, JDBC, Thrift, etc. Now the document seems like to mix them together so it could be hard for user to understand it.

### How should we improve?

reorganize content to reflect hierarchical relationship between different catalogs, so that user of each catalog can easy to understand what it is and how it works.

Start by locating the existing catalog documentation and reviewing how RESTful, JDBC, and Thrift catalogs are currently presented. Reorganize the content to show their hierarchy and give each catalog a clear explanation of what it is and how it works; done means users can understand the relationships without navigating mixed content.

Written by the indexing model from the issue text.