implement Apache APISIX echo plugin

APISIX currently provides a simple example plugin, but it does not provide useful functionality.

So we can provide a useful plugin to help users understand as fully as possible how to develop an APISIX plugin.

This plugin could implement the corresponding functionality in the common phases such as init, rewrite, access, balancer, header filer, body filter and log . But the specific functionality are still being considered.

Difficulty: Major

mentors: agile6v@ apache.org, wenming@apache.org, yousa@apache.org
Potential mentors:
Project Devs, mail: dev (at) apisix.apache.org