Better sampling override behavior

[trask]

(icm 577578458)

Currently, this configuration:

      {
        "telemetryType": "request",
        "attributes": [
          {
            "key": "http.url",
            "value": ".*/health-check",
            "matchType": "regexp"
          }
        ],
        "percentage": 0,
        "id": "filter out health check"
      },
      {
        "telemetryType": "dependency",
        "attributes": [
          {
            "key": "db.statement",
            "value": "select count(*) from abc",
            "matchType": "strict"
          }
        ],
        "percentage": 50,
        "id": "filter out noisy jdbc"
      }

has the unexpected effect of capturing 50% of select count(*) from abc calls, even when they occur within the excluded health check.

this PR updates the behavior so that when a sampling override percentage is <100 and a parent dropped, then the span (with override percentage < 100) will also be dropped

[jeanbisutti]

Could you please make the PR title more specific? Perhaps something like "Propagate the request sampling percentage"?

[jeanbisutti]

Because the scenarios are not super simple, the code comments could maybe try to refer to tests checking this scenario

[trask]

I totally agree that the scenarios are complex, this particular comment though I think it pretty clear (relatively, at least, compared to some of the other code in this PR)? maybe you had in mind other places?

[jeanbisutti]

My suggestion was to refer to tests in the comments, in addition to the current comment explanations.

[trask]

I'd prefer to just improve the comments if they are unclear. Or if you make specific suggestions linking these to tests I'm happy to hit accept.