Do not require a compileOnly configuration to be present

[timtebeek]

As reported via Slack:

* Where:
Build file '/Users/greg/git/rewrite/rewrite-bom/build.gradle.kts' line: 1

* What went wrong:
An exception occurred applying plugin request [id: 'org.openrewrite.build.publish']
> Failed to apply plugin 'org.openrewrite.build.publish'.
   > Configuration with name 'compileOnly' not found.

[greg-at-moderne]

I haven't tested it, but the defensive null-checks make sense.

The docs for findByName indeed indicate null response if not found:
https://docs.gradle.org/current/kotlin-dsl/gradle/org.gradle.api/-named-domain-object-collection/find-by-name.html