SpringBoot Replace deprecated method call in KotlinPluginAction.getKotlinVersion

This commit deprecated getKotlinPluginVersion and replaced it with fun Project.getKotlinPluginVersion(): String. We should ideally move to the new method.

Comment From: wilkinsona

I think we can safely make this change in 2.5 by calling KotlinPluginWrapperKt.getKotlinPluginVersion(project). It's been there for a while now.