chore: improve logging of reviewers (#29599)

lib/workers/repository/update/pr/participants.ts

@@ -73,17 +73,26 @@ export async function addParticipants(
   let reviewers = config.reviewers ?? [];
   if (config.reviewersFromCodeOwners) {
     reviewers = await addCodeOwners(config, reviewers, pr);
+    logger.debug(
+      `Reviewers from code owners: ${reviewers.map((reviewer) => `"${reviewer}"`).join(', ')}`,
+    );
   }
   if (
     is.array(config.additionalReviewers) &&
     config.additionalReviewers.length > 0
   ) {
+    logger.debug(
+      `Additional reviewers: ${config.additionalReviewers.map((reviewer) => `"${reviewer}"`).join(', ')}`,
+    );
     reviewers = reviewers.concat(config.additionalReviewers);
   }
   if (reviewers.length > 0) {
     try {
       reviewers = await prepareParticipants(config, reviewers);
       if (is.number(config.reviewersSampleSize)) {
+        logger.debug(
+          `Sampling reviewersSampleSize=${config.reviewersSampleSize} reviewers`,
+        );
         reviewers = sampleSize(reviewers, config.reviewersSampleSize);
       }
       if (reviewers.length > 0) {