Table INFORMATION_SCHEMA.ATTRIBUTES is not documented

[mjonss]

Change Request

Please answer the following questions before submitting your issue. Thanks!

1. Describe what you find is inappropriate or missing in the existing docs.
   https://docs.pingcap.com/tidb/stable/information-schema does not include ATTRIBUTES table

2. Describe your suggestion or addition.
   ATTRIBUTES table shows the Table Attributes, see https://docs.pingcap.com/tidb/stable/table-attributes

3. Provide some reference materials (such as documents and websites) if you could.
   First created under name REGION_LABEL
   ddl: support showing label rule through information schema table tidb#26637
   Then renamed to ATTRIBUTES
   ddl: rename region label to attributes tidb#29174

[Oreoxmt]

@rleungx Could you please take a look at this? Thanks!