Update docs for referenced_variable_metadata

[gerrycampion]

Documentation consistency and clarity:

• Updated output column prefixes for label_referenced_variable_metadata and name_referenced_variable_metadata to use the id value, ensuring outputs like $qlabel_referenced_variable_metadata_* and $qnam_referenced_variable_metadata_* match the provided id parameter. [1] [2]
• Renamed example rule id values for these operators to $qlabel_referenced_variable_metadata and $qnam_referenced_variable_metadata for consistency. [1] [2]
• Clarified that metadata column names in outputs are prefixed by the string provided in id, and updated descriptions for both operators. [1] [2]

Documentation organization:

• Moved the referenced_variable_metadata sections to be under IG and Model Var operations instead of the miscategorized Define XML ops. [1] [2]
• No changes to code logic—these are documentation-only improvements for clarity and maintainability. [1] [2]

[RamilCDISC]

updated as required.