feat(cmd/gf): add DaMeng database driver support

[Insua]

The purpose is to be able to use the DM database to build a CLI.

[Insua]

Certain databases, such as the DM (Dameng) database, enforce the rule that table names and column names must be in uppercase, especially when the database strictly differentiates between uppercase and lowercase. This strict enforcement helps to prevent numerous errors. However, with the current CLI tool, if the table names and column names are in uppercase, the generated struct names and field names will also be in all uppercase letters, which looks quite unattractive. To address this issue, I modified the code to convert all table names and column names to lowercase, resulting in more aesthetically pleasing and readable generated code.

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某些数据库（例如达梦数据库）要求表名和字段名严格遵循大写规范，尤其在数据库严格区分大小写的情况下。这种强制性规定避免了许多错误的产生。然而，在当前的CLI工具下，若表名和字段名是大写的，生成的结构体名称和字段名也会全为大写字母，显得非常不美观。为了解决这一问题，我对代码进行了修改，将表名和字段名全部转换为小写，使生成的代码更加美观和易于阅读