[SPARK-3296][mllib] spark-example should be run-example in head notation of DenseKMeans and SparseNaiveBayes

`./bin/spark-example`  should be `./bin/run-example` in DenseKMeans and SparseNaiveBayes

Author: wangfei <wangfei_hello@126.com>

Closes #2193 from scwf/run-example and squashes the following commits:

207eb3a [wangfei] spark-example should be run-example
27a8999 [wangfei] ./bin/spark-example should be ./bin/run-example

(cherry picked from commit 13901764f4e9ed3de03e420d88ab42bdce5d5140)
Signed-off-by: Xiangrui Meng <meng@databricks.com>