Only create a "config" instance if only it not yet created.

On one of the project I'm working right now, I'm using both Config and Capsule component, since I register config service location first and then capsule, all the preloaded config is destroy on the config service location is converted to instance of Illuminate\Support\Fluent which is not ideal in my use case.

Signed-off-by: crynobone <crynobone@gmail.com>
Merge pull request #4598 from crynobone/feature/capsule-config

[Database\Capsule] Only create a "config" instance if only it not yet created.