feat: add txn interceptor with gorm v2

[chinmayb]

This is a copy paste of https://github.com/infobloxopen/atlas-app-toolkit/blob/master/gorm/transaction.go

but using gorm.io library.

[chinmayb]

additional test cases for stream interceptor is added

[amaskalenka]

LGTM

You can also leverage db.Transaction method to get rid of the custom code for Commit and Rollback

var resp interface{}
terr := db.Transaction(func(tx *gorm.DB) error {
    ctx = NewContext(ctx, txn)
    r, err := handler(ctx, req)
    if err != nil {
        return err
    }
    resp = r
    return nil
})

if terr != nil {
     return nil, err
}

return resp, nil

[chinmayb]

@amaskalenka Good point! I will take it up as improvement and add it as a separate PR as I'd need to modify tests.

[chinmayb]

@amaskalenka just noticed that, there are commitHooks, that support will be lost if we use db.Transaction. So its better to keep it as it is ?

txn := &Transaction{parent: txn.parent, afterCommitHook: txn.afterCommitHook}