[13.x] Add minProperties and maxProperties to JsonSchema ObjectType

[hamdyelbatal122]

ArrayType already has min() / max() for minItems and maxItems. ObjectType was missing the same for property counts.

Adds min() and max() on ObjectType, same pattern as ArrayType.

[taylorotwell]

Thanks for your pull request to Laravel!

Unfortunately, I'm going to delay merging this code for now. To preserve our ability to adequately maintain the framework, we need to be very careful regarding the amount of code we include.

If applicable, please consider releasing your code as a package so that the community can still take advantage of your contributions!