🐛 Handle DNS resolution errors in ElastiCache discovery

[tas50]

Summary

• ElastiCache DescribeCacheClusters and DescribeServerlessCaches fail with "no such host" DNS errors in regions where ElastiCache endpoints don't resolve
• Added IsServiceNotAvailableInRegionError checks to both getCacheClusters and getServerlessCaches, matching the established pattern used by 12+ other AWS resources (memorydb, msk, opensearch, elb, cognito, etc.)
• Unavailable regions are now gracefully skipped with a debug log instead of failing the entire discovery

Test plan

• Build and install AWS provider (make providers/build/aws && make providers/install/aws)
• Run mql run aws -c "aws.elasticache.cacheClusters" — should no longer error on regions where ElastiCache DNS doesn't resolve
• Verify clusters are still returned from regions where ElastiCache is available

🤖 Generated with Claude Code

[mondoo-code-review]

ElastiCache discovery no longer fails when a region's DNS endpoint is unavailable.

[tas50]

Fixes discovery errors we get on the CLI right now:

x error during discovery error="operation error ElastiCache: DescribeCacheClusters, https response error StatusCode: 0, RequestID: , request send failed, Post \"https://elasticache.ap-south-1.amazonaws.com/\": POST https://elasticache.ap-south-1.amazonaws.com/ giving up after 3 attempt(s): Post \"https://elasticache.ap-south-1.amazonaws.com/\": dial tcp: lookup elasticache.ap-south-1.amazonaws.com: no such host\noperation error ElastiCache: DescribeCacheClusters, https response error StatusCode: 0, RequestID: , request send failed, Post \"https://elasticache.eu-north-1.amazonaws.com/\": POST https://elasticache.eu-north-1.amazonaws.com/ giving up after 3 attempt(s): Post \"https://elasticache.eu-north-1.amazonaws.com/\": dial tcp: lookup elasticache.eu-north-1.amazonaws.com: no such host\noperation error ElastiCache: DescribeCacheClusters, https response error StatusCode: 0, RequestID: , request send failed, Post \"https://elasticache.eu-west-3.amazonaws.com/\": POST https://elasticache.eu-west-3.amazonaws.com/ giving up after 3 attempt(s): Post \"https://elasticache.eu-west-3.amazonaws.com/\": dial tcp: lookup elasticache.eu-west-3.amazonaws.com: no such host\noperation error ElastiCache: DescribeCacheClusters, https response error StatusCode: 0, RequestID: , request send failed, Post \"https://elasticache.eu-west-2.amazonaws.com/\": POST https://elasticache.eu-west-2.amazonaws.com/ giving up after 3 attempt(s): Post \"https://elasticache.eu-west-2.amazonaws.com/\": dial tcp: lookup elasticache.eu-west-2.amazonaws.com: no such host\noperation error ElastiCache: DescribeCacheClusters, https response error StatusCode: 0, RequestID: , request send failed, Post \"https://elasticache.eu-west-1.amazonaws.com/\": POST https://elasticache.eu-west-1.amazonaws.com/ giving up after 3 attempt(s): Post \"https://elasticache.eu-west-1.amazonaws.com/\": dial tcp: lookup elasticache.eu-west-1.amazonaws.com: no such host\noperation error ElastiCache: DescribeCacheClusters, https response error StatusCode: 0, RequestID: , request send failed, Post \"https://elasticache.ap-northeast-3.amazonaws.com/\": POST https://elasticache.ap-northeast-3.amazonaws.com/ giving up after 3 attempt(s): Post \"https://elasticache.ap-northeast-3.amazonaws.com/\": dial tcp: lookup elasticache.ap-northeast-3.amazonaws.com: no such host\noperation error ElastiCache: DescribeCacheClusters, https response error StatusCode: 0, RequestID: , request send failed, Post \"https://elasticache.ap-northeast-2.amazonaws.com/\": POST https://elasticache.ap-northeast-2.amazonaws.com/ giving up after 3 attempt(s): Post \"https://elasticache.ap-northeast-2.amazonaws.com/\": dial tcp: lookup elasticache.ap-northeast-2.amazonaws.com: no such host\noperation error ElastiCache: DescribeCacheClusters, https response error StatusCode: 0, RequestID: , request send failed, Post \"https://elasticache.ap-northeast-1.amazonaws.com/\": POST https://elasticache.ap-northeast-1.amazonaws.com/ giving up after 3 attempt(s): Post \"https://elasticache.ap-northeast-1.amazonaws.com/\": dial tcp: lookup elasticache.ap-northeast-1.amazonaws.com: no such host\noperation error ElastiCache: DescribeCacheClusters, https response error StatusCode: 0, RequestID: , request send failed, Post \"https://elasticache.ca-central-1.amazonaws.com/\": POST https://elasticache.ca-central-1.amazonaws.com/ giving up after 3 attempt(s): Post \"https://elasticache.ca-central-1.amazonaws.com/\": dial tcp: lookup elasticache.ca-central-1.amazonaws.com: no such host\noperation error ElastiCache: DescribeCacheClusters, https response error StatusCode: 0, RequestID: , request send failed, Post \"https://elasticache.sa-east-1.amazonaws.com/\": POST https://elasticache.sa-east-1.amazonaws.com/ giving up after 3 attempt(s): Post \"https://elasticache.sa-east-1.amazonaws.com/\": dial tcp: lookup elasticache.sa-east-1.amazonaws.com: no such host"
 /aws/lambda/MondooUpdater                                                                                   ━━━━━━━━━━━━━━━━━━━━━━ 100% score: HIGH

[github-actions]

Test Results

5 450 tests  ±0   5 446 ✅ ±0   2m 31s ⏱️ +12s
  412 suites ±0       4 💤 ±0 
   31 files   ±0       0 ❌ ±0 

Results for commit 2dce76c. ± Comparison against base commit e29a520.