let gorm support limit and offset binding parameters,change the BindVar of postgres driver

[jasonchuan]

if limit and offset use the parameter in new gorm version，must remove config vars before bindvar to ,and then restore them.

• [x] Do only one thing
• [x] Non breaking API changes
• [x] Tested

What did this pull request do?

User Case Description

this is necessary for limit and offset binding parameters issue https://github.com/go-gorm/gorm/pull/6806

[jasonchuan]

@jinzhu please approve this commit first and add a tag for this version next step https://github.com/go-gorm/gorm/pull/6806