fix: Target and Network error with Dashboard in Docker Compose

[JaredforReal]

What this PR does / why we need it:

• fix target error in Grafana and Prometheus
• update README.

left issue CORS with Grafana in Dashboard

[github-actions]

👥 vLLM Semantic Team Notification

The following members have been identified for the changed files in this PR and have been automatically assigned:

📁 dashboard

Owners: @JaredforReal, @Xunzhuo
Files changed:

• dashboard/README.md

📁 deploy

Owners: @rootfs, @Xunzhuo
Files changed:

• deploy/docker-compose/README.md
• deploy/docker-compose/docker-compose.yml

📁 tools

Owners: @yuluo-yx, @rootfs, @Xunzhuo
Files changed:

• tools/observability/grafana-datasource.yaml
• tools/observability/prometheus.yaml

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🎉 Thanks for your contributions!

This comment was automatically generated based on the OWNER files in the repository.

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