[config,metrics] Move metrics configuration section under respective NF section

Without this change, using metrics with core setup configurations
(configs/vonr.yaml for example) would not be possible. Having one
metrics section for whole config file causes every NF to start metrics
server on same port causing an abort.

lib/metrics/void/context.c

@@ -50,7 +50,7 @@ ogs_metrics_context_t *ogs_metrics_self(void)
     return &self;
 }
 
-int ogs_metrics_context_parse_config(void)
+int ogs_metrics_context_parse_config(const char *local)
 {
     return OGS_OK;
 }