Updated promtail git tag for system(d) log support

Package Merge Request

Package Changes

https://repo1.dso.mil/big-bang/apps/sandbox/promtail/-/blob/6.8.1-bb.1/CHANGELOG.md

Package MR

https://repo1.dso.mil/big-bang/apps/sandbox/promtail/-/merge_requests/24

For Issue

Closes #1387 (closed)