Remove Promtail

General MR

Summary

This MR removes Promtail from Big Bang as a supported package.

Relevant logs/screenshots

Linked Issue

closes #2781 (closed)

Upgrade Notices

Promtail has been officially removed as a log aggregator in Big Bang pursuant to its deprecation by Grafana Labs. The Promtail project has been merged into the Grafana Alloy project upstream and integrated into Big Bang as the alloy package. Alloy is the default log aggregation tool since Big Bang 3.0. Promtail will move to community supported packages. Promtail is scheduled upstream for end of life date of March 2, 2026. If the community does not maintain the Promtail package it will be archived from Repo1 sooner. Users can still deploy the Promtail using the packages section of the umbrella values by modifying Big Bang values.yaml under the packages: key.