DatabaseRewrites Config option to rename schema is incorrect

[NatMorcos]

The Config suggests a top level option in the .json file passed into the ghostferry-copydb process on initialization:

ghostferry/config.go

Lines 355 to 361 in 5f71469

	// Map database name on the source database (key of the map) to a
	// different name on the target database (value of the associated key).
	// This allows one to move data and change the database name in the
	// process.
	//
	// Optional: defaults to empty map/no rewrites
	DatabaseRewrites map[string]string

However, this is incorrect. This option is never accessed. The copydb process expects a nested option inside a top level Database key:

ghostferry/copydb/config.go

Lines 24 to 27 in 5f71469

	// Allows database/tables to be renamed from source to the target, where the
	// key of this map is the database/table names on the source database and the
	// value of the map is on the database/table names target database.
	Rewrites map[string]string

A successful config file using this option should look like

# Good

{
  "Source": { ...  },
  "Target": { ...  },
  "Databases": {
     # ...
    "Rewrites": {
      "old_schema_name": "new_target_schema_name"
    }
  },
  "Tables": { ... },
  # Other top level options
}

The documentation + the /config.go file suggest

# Bad

{
  "Source": { ...  },
  "Target": { ...  },
  "Databases": { ...  },
  "Tables": { ... },
  "DatabaseRewrites: {
      "old_schema_name": "new_target_schema_name"
    },
  # Other top level options
}