Add enum fields in columnInfo

[Idered]

I need to get possible enum values for given column.

This PR extends inspector.columnInfo('table') with

• udt_name - user defined type. For enums this will return enum name, for other types it will return type name eg. varchar
• enum_values - if column is enum then this will be an array of possible values

Example result for inspector.columnInfo('user', 'role'):

{ 
    name: 'role',
    table: 'user',
    type: 'USER-DEFINED',
    udt_name: 'user_role_enum', // NEW
    enum_values: [ 0, 1 ], // NEW
    default_value: 0,
    max_length: null,
    precision: null,
    scale: null,
    is_nullable: true,
    is_primary_key: false,
    has_auto_increment: false,
    foreign_key_column: null,
    foreign_key_table: null,
    comment: null,
    schema: 'public',
    foreign_key_schema: null 
}

TODO:

• PostgreSQL
• MySQL
• MSSQL
• OracleDB
• SQLite