Create writeClasspathUniquenessLock task that can be used instead of --write-locks

[ash211]

What happened?

Users want to run a specific command to update just the classpath uniqueness lock file, instead of --write-locks which updates all files.

What did you want to happen?

The same way that palantir/gradle-consistent-versions#723 added gw writeVersionsLock to update just versions.lock, this issue is for a task named something like gw writeClasspathUniquenessLock to update just baseline-class-uniqueness.lock.