Move all admin APIs to information_schema or implement them as SQL function

[killme2008]

What type of enhancement is this?

Tech debt reduction, User experience

What does the enhancement do?

Before we make improvements for information_schema in #2931 , we designed some HTTP APIs under /admin to query table metadata or routes etc.

Some APIs such as /tables,/schemas are already supported by infomration_schema.tables or infomration_schema.schamta virtual tables. Others can be moved into infomration_schema too, for example, the table routes info.

Also, we can implement SQL functions to support some management APIs such as migrating regions.

Implementation challenges

No response