3.6.0: `block_builder` config item causes startup errors

[agross]

Describe the bug

block_builder:
  max_chunk_age: 18000h

failed parsing config: /etc/loki/local-config.yaml: yaml: unmarshal errors:
  line 3: field block_builder not found in type loki.ConfigWrapper. Use `-config.expand-env=true` flag if you want to expand environment variables in your config file

To Reproduce
Steps to reproduce the behavior:

1. Start Loki 3.6.0 with the config above that worked in 3.5.8
2. Expected to find something causing this in the release notes, but didn’t
3. Expected to find 3.6.x docs, but didn't

Expected behavior

3.6.0 works like 3.5.8

Environment:

• Infrastructure: docker
• Deployment tool: docker compose