loki update to 5.31.0-bb.0 & promtail update to 6.15.3-bb.0

Package Merge Request

Package Changes

(Describe Package changes here)

Package MR

big-bang/product/packages/loki!105 (merged)

big-bang/product/packages/promtail!44 (merged)

For Issue

Closes big-bang/product/packages/loki#66 (closed)

Closes big-bang/product/packages/promtail#28 (closed)