missing documentation for 'custom_name' configuration option

`custom_name` ([in the server API](https://hasura.io/docs/latest/graphql/core/api-reference/syntax-defs.html#table-config)) is exposed in the console as `Custom Table Name` but we currently do not have any documentation on what this actually does. We do have documentation for [other customization options](https://hasura.io/docs/latest/graphql/core/databases/postgres/schema/custom-field-names.html).