Can MetricWriter and MetricReader be abstracted into interfaces and support SPI extensions?

## Issue Description

Type: *feature request*

### Describe what feature you want

MetricWriter ,MetricReader,MetricsReader 这三个抽象成接口,支持SPI扩展,方便用户自定义扩展存储方式。

Make MetricWriter, MetricReader and MetricsSearcher SPI extension interfaces so that users can implement their own metrics storage.

Start by locating MetricWriter, MetricReader, and MetricsSearcher in the Java source and inspect how metrics storage is currently connected. Clarify the MetricsReader/MetricsSearcher naming discrepancy, then determine the SPI extension boundary; done means users can implement custom metrics storage through the requested interfaces.

Written by the indexing model from the issue text.