**Describe the bug**
A clear and concise description of what the bug is.

我使用了retain持久化配置
sqlite {
    disk_cache_size = 102400
    mounted_file_path = "/usr/local/etc/"
    flush_mem_threshold = 100
    resend_interval = 5000
}

使用桥接功能，当从emqx发送 retain 消息桥接到nanomq
Topic: /node/ad345be3b320d/t123QoS: 0
{"msg": "ret111"}

Topic: /node/ad345be3b320d/t123QoS: 0
{"msg": "ret222"}

Topic: /node/ad345be3b320d/t123QoS: 0
{"msg": "ret333"}

nanomq的客户端连接后都是拿到消息：{"msg": "ret111"}  只有重启nanomq，nanomq的客户端连接后才能拿到消息{"msg": "ret333"}

How to preserve retain flag in bridging?
This is a GitHub Issue
repo:nanomq
owner:emqx
Title : How to preserve retain flag in bridging?
Issue date:

--- start body ---
**Describe the bug**
A clear and concise description of what the bug is.

我使用了retain持久化配置
sqlite {
    disk_cache_size = 102400
    mounted_file_path = "/usr/local/etc/"
    flush_mem_threshold = 100
    resend_interval = 5000
}

使用桥接功能，当从emqx发送 retain 消息桥接到nanomq
Topic: /node/ad345be3b320d/t123QoS: 0
{"msg": "ret111"}

Topic: /node/ad345be3b320d/t123QoS: 0
{"msg": "ret222"}

Topic: /node/ad345be3b320d/t123QoS: 0
{"msg": "ret333"}

nanomq的客户端连接后都是拿到消息：{"msg": "ret111"}  只有重启nanomq，nanomq的客户端连接后才能拿到消息{"msg": "ret333"}

--- end body ---
