Support CWAGENT_ROLE env var for Container Insights mode in JSON v2 config

[Paamicky]

Description of the issue

The OTel Container Insights pipeline had no defined priority order for resolving the pipeline mode. The getMode function returned "" when no mode was configured, leaving callers to implicitly treat an empty string as "node". There was also no way for the Helm chart to set the mode without an explicit JSON config change

Description of changes

Introduces a defined priority order for resolving the Container Insights pipeline mode:

• JSON config field (mode) takes highest precedence
• CWAGENT_ROLE environment variable: used by the Helm chart to indicate whether the agent runs as a DaemonSet (NODE) or Deployment (LEADER)
• Default: "node": if neither is set, the agent defaults to DaemonSet/node mode

The getMode function is updated to implement this priority order explicitly. The NewTranslators function is updated to use named constants (modeNode, modeCluster) instead of bare string comparisons, and a nil/missing-key guard is added to return early with zero translators if the container_insights config key is not present.

License

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Tests

Added unit tests covering all priority order cases:

• TestGetMode_JSONConfig: mode read from JSON config
• TestGetMode_EnvVarFallback: env var used when JSON config has no mode set
• TestGetMode_DefaultsToNode: defaults to "node" when neither config nor env var is set
• TestGetMode_JSONOverridesEnv: JSON config wins when both are present
• TestNewTranslators_MissingKey: returns zero translators for nil/empty config

Requirements

1. Run make fmt and make fmt-sh
2. Run make lint