feat(publish-metrics): implement smartSampling for Playwright tracing

[InesNi]

Description

This PR introduces two main changes:

1. smartSampling support for the Playwright engine tracing.

If smartSampling is configured in the test script (as shown below), only traces that have recorded errors will be exported.

  plugins:
    publish-metrics:
      - type: open-telemetry
        traces:
          smartSampling: {}

2. A breaking change is introduced in the smartSampling configuration for the HTTP engine.

The additional optional threshold settings will now be nested inside the http key:

Old config:

  plugins:
    publish-metrics:
      - type: open-telemetry
        traces:
          smartSampling:
            thresholds:
              firstByte: 500
              total: 2000

New config:

  plugins:
    publish-metrics:
      - type: open-telemetry
        traces:
          smartSampling:
            http:
              thresholds:
                firstByte: 500
                total: 2000

Testing

Tested manually by running multiple scenarios with different settings, viewing results on different observability platforms, running locally and with Fargate. All seems to be running properly. See screenshots for one of the tests below

Pre-merge checklist

• Does this require an update to the docs?
• Does this require a changelog entry?