Docs: improve documentation to explain how to configure the split-and-merge compactor

[songjiayang]

Is your documentation request related to a feature? If so, which one?

When I followed Mimir's tutorial to practice, it started quickly，this is very helpful for the overall understanding of Mimir. But when I wanted to test split merge compacting function, it taked a lot of time.

Describe the solution that you’d like or the expected outcome

adding demo tenant overrides example.

Step 1: add runtime_config to play-with-grafana-mimir/config/mimir.yaml

runtime_config:
  file: /etc/overrides.yaml

Step2: add play-with-grafana-mimir/config/overrides.yaml

overrides:
  demo:
    compactor_split_and_merge_shards: 2
    compactor_split_groups: 2

Step3: update play-with-grafana-mimir/docker-compose.yml, add ./config/overrides.yaml:/etc/overrides.yaml to mimir-[1-3]'s volumes.

mimir-1/2/3:
    image: grafana/mimir:latest
    command: ["-config.file=/etc/mimir.yaml"]
    hostname: mimir-1
    depends_on:
      - minio
    volumes:
      - ./config/mimir.yaml:/etc/mimir.yaml
      -  ./config/overrides.yaml:/etc/overrides.yaml
      - ./config/alertmanager-fallback-config.yaml:/etc/alertmanager-fallback-config.yaml
      - mimir-1-data:/data

[t00350320]

It helps me a lot.

[pracucci]

Thanks for opening this issue! I agree we should better document how to configure the split-and-merge compactor. I wouldn't do it in the tutorial, because the purpose of the tutorial is to show the simplest Mimir HA installation possible, but we could add create a new dedicated doc page on how to configure the compactor under docs/sources/operators-guide/configure and make sure it's linked from docs/sources/operators-guide/architecture/components/compactor/index.md and there's no duplicated content between the two.

[songjiayang]

Sounds great