[NOTICKET] metrics: enable fluentbit local buffer to avoid metrics loss

when fluentbit loses connection to the metrics endpoint (open telemetry), unsent metrics are dropped and permanently lost. This commit enables the local buffering feature in Fluent Bit, allowing metrics to be temporarily stored in a local buffer. When the connection is reestablished, these buffered metrics are retried and sent to the endpoint. This improves reliability by minimizing metric loss during intermittent connection issues.

Proposed-by: Nacho Barrientos <nacho.barrientos@cern.ch>