In the read-write separation scenario, a switch for the session-level enable weakly consistent read or only for the session-level enable weakly consistent read to the specified user

[justdba]

读写分离场景，为指定obproxy开启会话级别弱一致性读（连接该obproxy默认开启ob_read_consistency=WEAK）,或仅为指定用户开启会话级别弱一致性读