Correlating Subseries with labels，时序列打标签功能

功能描述：
（1）为给定时序列，指定时间戳范围的时序数据，定义标签名称：即用户指定序列、指定起始时间、结束时间、标签，数据库成功将标签与相关时序列段进行关联
（2）用户可以根据标签找到相关时序数据

Functional Description:
(1) a user provides time series path, start timestamp, end timestamp, a label, the TSDB should correlate the label with the subseries identified by the first three parameters
(2) users can later locate the subseries by the label

Start by reviewing the functional description and the existing IoTDB interfaces for time-series operations. Define how a user supplies a time-series path, start and end timestamps, and a label, then verify that labeled subseries can later be located by that label.

Written by the indexing model from the issue text.