Fix many to many polymorphic pivot updates

`$morphType ` set by `setMorphType` is being included in queries from x->pivot->save() and the like. As the object is being added as a public data member on an object with an empty original, it is treated as an attribute and added as a column to the queries. As this column doesn't exist, the query will be erroneous.

https://github.com/laravel/framework/issues/3693
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 #4288 from skovacs1/4.1

[Bug] Fix many to many polymorphic pivot updates
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