Error trying to build grafana container

While trying to build the grafana container using the provided files in the lodestar repository, I get the following error:

```
~/lodestar$ sudo docker compose up -d grafana
WARN[0000] /home/ubuntu/lodestar/docker-compose.yml: the attribute `version` is obsolete, it will be ignored, please remove it to avoid potential confusion
[+] Building 1.5s (6/6) FINISHED docker:default
=> [grafana internal] load build definition from Dockerfile 0.0s
=> => transferring dockerfile: 897B 0.0s
=> [grafana] resolve image config for docker-image://docker.io/docker/dockerfile:1.4 0.7s
=> CACHED [grafana] docker-image://docker.io/docker/dockerfile:1.4@sha256:9ba7531bd80fb0a858632727cf7a112fbfd19b17e94c4e84ced81e24ef1a0dbc 0.0s
=> [grafana internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> ERROR [grafana internal] load metadata for docker.io/library/dashboards:latest 0.5s
=> CANCELED [grafana internal] load metadata for docker.io/grafana/grafana:latest 0.5s
------
> [grafana internal] load metadata for docker.io/library/dashboards:latest:
------
failed to solve: failed to resolve source metadata for docker.io/library/dashboards:latest: pull access denied, repository does not exist or may require authorization: server message: insufficient_scope: authorization failed
```

I believe the issue is in the following [line](https://github.com/ChainSafe/lodestar/blob/a7286bd669e659e3baff38254c118066f49269dc/docker/grafana/Dockerfile#L11) of the docker/grafana/Dockerfile file.

The `COPY --from=dashboards` syntax is mainly used during a multi-stage build, that's why it fails with the message of " docker.io/library/dashboards:latest: pull access denied, repository does not exist or may require authorization"

Steps to reproduce

1- Delete any previous lodestar-grafana images
` sudo docker rmi lodestar-grafana
Untagged: lodestar-grafana:latest
Deleted: sha256:0ddee6fbd6a27951a9c9c2b00313e600d733b76d9ee60181a613f712c1074edf
`
2- Start the grafana service
`~/lodestar$ sudo docker compose up -d grafana`