Add resource readers from service providers in CLI (#1581)

This omission, in particular, prevents Gradle plugins (which rely on CLI
classes) from adding custom resource readers via the service loading
mechanism. This change seems benign, especially since this is already
done for module key factories.

pkl-commons-cli/src/main/kotlin/org/pkl/commons/cli/CliCommand.kt

@@ -307,6 +307,7 @@ abstract class CliCommand(protected val cliOptions: CliBaseOptions) {
       add(ResourceReaders.modulePath(modulePathResolver))
       add(ResourceReaders.pkg())
       add(ResourceReaders.projectpackage())
+      addAll(ResourceReaders.fromServiceProviders())
       add(ResourceReaders.file())
       add(ResourceReaders.http())
       add(ResourceReaders.https())