Document required pipeline exporter configuration for openobserve-collector 0.4.0

[Copilot]

PR #168 removed default exporters from pipelines but the README lacks documentation for the now-required pipeline configuration values.

Changes

• Added Configuration section to charts/openobserve-collector/README.md with complete example values.yaml
• Documents both exporter definitions and pipeline exporter references for agent and gateway

Example values.yaml

exporters:
  otlphttp/openobserve:
    endpoint: http://o2-openobserve-router.openobserve.svc.cluster.local:5080/api/default
    headers:
      Authorization: "Basic <token>"
  otlphttp/openobserve_k8s_events:
    endpoint: http://o2-openobserve-router.openobserve.svc.cluster.local:5080/api/default
    headers:
      Authorization: "Basic <token>"
      stream-name: k8s_events

agent:
  service:
    pipelines:
      logs:
        exporters:
          - otlphttp/openobserve
      metrics:
        exporters:
          - otlphttp/openobserve

gateway:
  service:
    pipelines:
      logs/k8s_events:
        exporters:
          - otlphttp/openobserve_k8s_events
      logs/k8s_pods:
        exporters:
          - otlphttp/openobserve
      metrics:
        exporters:
          - otlphttp/openobserve
      traces:
        exporters:
          - otlphttp/openobserve
          - servicegraph

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Helm chart of openobserve-collector 0.4.0 breaks the default config</issue_title>
<issue_description>In #168, the exporters defined in pipelines are removed. But the instructions of deploying the collector both in o2 data sources panel and the README of the chart repo lacks the additional required values.

The following values need to be added if using the latest chart:

# Previously only the following are needed
exporters:
  otlphttp/openobserve:
    endpoint: http://o2-openobserve-router.openobserve.svc.cluster.local:5080/api/default
    headers:
      Authorization: Basic <token>
  otlphttp/openobserve_k8s_events:
    endpoint: http://o2-openobserve-router.openobserve.svc.cluster.local:5080/api/default
    headers:
      Authorization: Basic <token>
      stream-name: k8s_events # This line also needs to be added

# Newly required
agent:
  service:
    pipelines:
      logs:
        exporters:
          - otlphttp/openobserve
      metrics:
        exporters:
          - otlphttp/openobserve

gateway:
  service:
    pipelines:
      logs/k8s_events:
        exporters:
          - otlphttp/openobserve_k8s_events
      logs/k8s_pods:
        exporters:
          - otlphttp/openobserve
      metrics:
        exporters:
          - otlphttp/openobserve
      traces:
        exporters:
          - otlphttp/openobserve
          - servicegraph
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes Helm chart of openobserve-collector 0.4.0 breaks the default config #170

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