[SPARK-16020][SQL] Fix complete mode aggregation with console sink

## What changes were proposed in this pull request?

We cannot use `limit` on DataFrame in ConsoleSink because it will use a wrong planner. This PR just collects `DataFrame` and calls `show` on a batch DataFrame based on the result. This is fine since ConsoleSink is only for debugging.

## How was this patch tested?

Manually confirmed ConsoleSink now works with complete mode aggregation.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #13740 from zsxwing/complete-console.