feat(error-tracking): add settings for backend standalone

[GianlucaBortoli]

What this PR does / why we need it:

Exposes new settings available for the agent:

• agents.coreAgent.enabled controls Add infra agent config option datadog-agent#30137
• datadog.apm.errorTrackingStandalone.enabled controls Add Error Tracking Standalone Config option datadog-agent#30065

The equivalent for the operator will be done in a separate PR.

Checklist

• Chart Version bumped
• Documentation has been updated with helm-docs (run: .github/helm-docs.sh)
• CHANGELOG.md has been updated
• Variables are documented in the README.md
• For Datadog Operator chart or value changes update the test baselines (run: make update-test-baselines)

[clamoriniere]

It doesn’t seem ideal to base the activation or deactivation of a feature on a container name (coreAgent). While this approach has been used in the past, we are now aiming to define settings names based on the end-user feature rather than internal or technical details.

Additionally, the proposed setting name feels too generic. It would be preferable to use a name that is both clear and self-explanatory. For example, something along the lines of agents.payloadForwarder.enabled or, considering the functionality in the datadog-agent codebase, agents.metricsForwarder.enabled might be more appropriate.

WDYT?

[clamoriniere]

I don’t feel knowledgeable enough yet about this new APM feature to recommend the best approach for enabling the "error tracking standalone" functionality.

However, if the APM team intends to reuse the datadog Helm chart while enabling only this APM feature, simply disabling the metrics forwarder doesn’t seem optimal. This is because several other functionalities currently run by default in the core-agent or process-agent container and would continue to execute within the core-agent process, consuming CPU and memory resources unnecessarily. We also run by default the cluster-agent component.