add example for CallablePreparedStatement

[vagetablechicken]

CallablePreparedStatement -> RequestPreparedStatement -> PreparedStatement
It can do

stmt = create()
for i:
  stmt.setXX()
  stmt.executeQuery() # in dataBuild, it'll clearParameters()

• Add a best practice and ut for it.

It's not good to create the stmt every time, cuz ctor is a little complex.

OpenMLDB/java/openmldb-jdbc/src/main/java/com/_4paradigm/openmldb/jdbc/CallablePreparedStatement.java

Line 31 in f349d72

public CallablePreparedStatement(String db, String spName, SQLRouter router) throws SQLException {