Summary: Fix yb-collect_metrics.service not starting due to missing yb_metrics_dir path in collect_metrics_wrapper.sh script

Test Plan: Manually tested in dev server

Reviewers: anijhawan, svarshney

Reviewed By: svarshney

Subscribers: anijhawan, rtsisyk, svarshney

Differential Revision: https://phorge.dev.yugabyte.com/D44484