Force UTF-8 Encoding for PostgreSQL Backend Connections in ShardingSphere-Proxy

[ShenFeng312]

Feature Request

see
https://github.com/pgjdbc/pgjdbc/blob/master/pgjdbc/src/main/java/org/postgresql/core/v3/SimpleParameterList.java#L553-L555
in pg jdbc

In pgjdbc, strings are always transmitted as UTF-8, regardless of any character set settings on the client or in the JDBC URL. The database still decodes the received bytes according to the client's client_encoding, and then converts them to its internal storage encoding.

Java Client String
        │ encode (UTF-8, forced)
        │  ← ignores client/JDBC character set settings
        ▼
     Byte Stream (always UTF-8)
        │
        ▼
PostgreSQL Server
        │ decode using client_encoding
        ▼
Database Internal Storage Encoding