promtail update to 6.15.5-bb.4

Package Merge Request

Package Changes

https://repo1.dso.mil/big-bang/product/packages/promtail/-/blob/6.15.5-bb.4/CHANGELOG.md

Package MR

big-bang/product/packages/promtail!77 (merged)

For Issue

Closes big-bang/product/packages/promtail#46 (closed)

Upgrade Notices

N/A