✨ feat(scalafmt): enforce version consistency between library and config file

[gaeljw]

Closes #2460

As suggested in #2460 (comment), this is a first step to raise awareness to users that the version declared in the config file is not used.

We might work on dynamically loading the right Scalafmt JAR in another PR.

I've tested this locally on a project of mine and this works, when versions are not aligned I got the following error:

[ERROR] Failed to execute goal com.diffplug.spotless:spotless-maven-plugin:2.44.5-SNAPSHOT:check (default-cli) on project xxx: Unable to check file /home/xxx/src/test/scala/bdd/utils/DataTableTypeMappings.scala: java.lang.reflect.InvocationTargetException: Spotless is using 2.7.5 but the config file declares 3.9.6. Both must match. Update the version declared in the plugin's settings and/or the config file. 

[gaeljw]

@nedtwigg no rush but any chance you could have a look at this?

[nedtwigg]

Released in plugin-gradle 7.1.0 and plugin-maven 2.45.0.