Add new statistical aggreators include stddev and variance.

Many databases like MySQL, PostgreSQL, Trino and Doris have already support built-in statistical aggreators like stddev and variance, while currently IoTDB has not. Hence we decide to write similar aggreators to extends IoTDB's aggression functionality.

More details can be seen in https://lz8h91usu0.feishu.cn/docx/HJt3dWEBooYAL1xvkknciTswnPc?from=from_copylink