refactor: Update PHPDoc Common::config

[maniaba]

Description
The @template annotation relates to a concept called Generics, which does not currently exist in PHP, but are a way of dynamically describing the contents of a parameter or return type that would be unknown until a class is instantiated or method called.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[kenjis]

Thank you for sending PR.

Please sign all your commits:
https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/pull_request.md#signing
https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/workflow.md#gpg-signing-old-commits

Fix the coding style:
https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/pull_request.md#php-style

Fix PHPStan errors:
https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/pull_request.md#static-analysis-on-php-code

[kenjis]

This is the same thing as model(), and works with PhpStorm.

[kenjis]

@maniaba Thank you.

We will accept the change from config('Foo') to config(Foo::class) in everywhere.