Add sparkbar aggregate function with noted future changes

Why it matters

The sparkbar function provides a compact visualization of aggregate data, enabling users to generate concise sparkbar-style summaries directly within their queries. This helps in quickly analyzing trends or distributions in aggregated datasets without external visualization tools.

How to use it

Use the sparkbar aggregate function within your query's SELECT clause to compute sparkbar representations of data. Example usage might look like:

SELECT sparkbar(column_name) FROM table_name;

Note that the function's behavior may change in future releases as it is currently experimental.