Add comments pointing to Azure creds renewal docs (#127897)

These were some of the places I looked for information about renewal.
Leaving a hint for next time.

Author: DaveCTurner

.buildkite/scripts/third-party-test-credentials.sh

@@ -7,6 +7,7 @@ set -euo pipefail
 # The second/lowercase export is what the tests expect/require
 
 if [[ "${USE_3RD_PARTY_AZURE_CREDENTIALS:-}" == "true" ]]; then
+  # These credentials expire periodically and must be manually renewed - the process is in the onboarding/process docs.
   json=$(vault read -format=json secret/ci/elastic-elasticsearch/migrated/azure_thirdparty_test_creds)
 
   AZURE_STORAGE_ACCOUNT_SECRET=$(echo "$json" | jq -r .data.account_id)
@@ -19,6 +20,7 @@ if [[ "${USE_3RD_PARTY_AZURE_CREDENTIALS:-}" == "true" ]]; then
 fi
 
 if [[ "${USE_3RD_PARTY_AZURE_SAS_CREDENTIALS:-}" == "true" ]]; then
+  # These credentials expire periodically and must be manually renewed - the process is in the onboarding/process docs.
   json=$(vault read -format=json secret/ci/elastic-elasticsearch/migrated/azure_thirdparty_sas_test_creds)
 
   AZURE_STORAGE_ACCOUNT_SECRET=$(echo "$json" | jq -r .data.account_id)

modules/repository-azure/src/internalClusterTest/java/org/elasticsearch/repositories/azure/AzureStorageCleanupThirdPartyTests.java

@@ -48,6 +48,10 @@
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.not;
 
+/**
+ * These tests sometimes run against a genuine Azure endpoint with credentials obtained from Vault. These credentials expire periodically
+ * and must be manually renewed; the process is in the onboarding/process docs.
+ */
 public class AzureStorageCleanupThirdPartyTests extends AbstractThirdPartyRepositoryTestCase {
     private static final Logger logger = LogManager.getLogger(AzureStorageCleanupThirdPartyTests.class);
     private static final boolean USE_FIXTURE = Booleans.parseBoolean(System.getProperty("test.azure.fixture", "true"));