make Model::paginate() use default perPage from Config\Pager->perPage if $perPage parameter not passed

[samsonasik]

Currently, the $perPage is default to 20 in Model::paginate() function. I think it should read from config('Pager')->perPage instead. I apply make default to null, and check if it is not passed, it will use the default config('Pager')->perPage

Checklist:

• Securely signed commits
• Unit testing, with >80% coverage

[samsonasik]

I've added unit test for use case change config('Pager')->perPage and passed parameter

[samsonasik]

travis build green 🎉

[samsonasik]

I've added check in Pager class to read $perPage from Config('Pager')->perPage to handle it when used in outside Model/Db related pagination.

[samsonasik]

I moved the handle per page null check to Pager class, use $this->pager->getPerPage() pulled from Pager instance to get final perPage value that will be used to make a limit query in the Model::paginate()

[samsonasik]

I updated CodeIgniter\Config\Services::pager() to use config('Pager') as well if no $config passed (null), instead of manual "new Config\Pager()" like in other services which uses config() function. It also make it testable in paginate in model test.

[samsonasik]

travis build green 🎉

[MGatner]

Definitely a good change, and a solid PR. Thanks as always @samsonasik