make conf.SortByPk configurable

[lichunzhu]

Feature Request

Is your feature request related to a problem? Please describe:

In dumpling we have variable conf.SortByPk. When it's false, dumpling won't add order by clause after the original select SQL. However, it's always set to true and not configurable now.

Describe the feature you'd like:

make conf.SortByPk configurable
The argument could be either --order-by-pk, --sort-by-pk, --order

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Optimization:

[lichunzhu]

Relative problem: https://asktug.com/t/topic/67660/8

Open this argument may cause lightning to insert data without order. Need more estimation to do this.