Update Big Bang Docs to Replace Promtail with Alloy

Need to update the Big Bang docs to reflect deprecating Promtail and moving to Alloy as default.

Update/replace (or remove, if OBE) examples:

• docs/guides/using-bigbang/autoscaling-fluentbit-and-promtail.md
  • CONFIRMED VPA repo is no longer maintained.
• docs/guides/using-bigbang/efk-plg-logging-migration.md
• docs/guides/deployment-scenarios/appliance-mode.md
  • Check if "appliance-mode" still recommended lightweight deployment strategy, delete file if not.
  • Appliance mode is not referenced in the BB Deployment Scenarios
• docs/assets/configs/appliance-mode/values.yaml
  • Check if "appliance-mode" still recommended lightweight deployment strategy, delete file if not.
  • Appliance mode is not referenced in the BB Deployment Scenarios
• docs/guides/using-bigbang/image-pull-policy.md
  • OPINION: Page feels redundant to values.yaml/readme and will never be kept up to date.
• docs/packages.md
  • OPINION: Consider replacing with URL to folders containing the templates, or removing URLs entirely.
    • Also worth noting theres inconsistencies where many MR URLs link to the Umbrella chart bump, and others link to the package MR with the actual changes.
• docs/understanding-bigbang/configuration/base-config.md
  • This looks auto generated, skipping.
• docs/understanding-bigbang/package-architecture/README.md
• docs/understanding-bigbang/package-architecture/twistlock.md
• docs/understanding-bigbang/package-architecture/loki.md
• docs/understanding-bigbang/package-architecture/tempo.md
• docs/understanding-bigbang/package-architecture/argocd.md
• docs/understanding-bigbang/package-architecture/promtail.md
• docs/developer/ironbank-testing.md
  • Check if this process is still used/followed, delete if not.
• docs/guides/deployment-scenarios/quickstart.md
• docs/assets/configs/example/git-repo-values.yaml (may be stale/unneeded)
  • OPINION: Delete this file
• docs/assets/configs/example/core-packages-1-x.yaml (may be stale/unneeded)
  • OPINION: Delete this file

Add deprecation note:

• docs/understanding-bigbang/package-architecture/promtail.md