[fix]: Improve error logging for metric insertion failures in dogstatsd

[litianningdatadog]

Improve error logging for metric insertion failures in dogstatsd

https://datadoghq.atlassian.net/browse/SVLS-8464

Motivation

While warning message is logged when batch insertion of metrics fails, it is unclear which metric/metrics are impacted. Hence we introduced this change to improve observability

• Fix use-after-move error by capturing metric name before insert
• Log both metric name and error details when insertion fails
• Add test case to verify overflow error handling

Testing

• Unit test
• Tested with bottlecap

1. Test function
2. Logs