RUM-6850: Add "Effective Sample Rate" to telemetry events

[simaoseica-dd]

What and why?

This PR adds a new property effectiveSampleRate to all types of telemetry events.
We want to know the actual rate applied to the events that is composed by all the sample rates, in the different layers, through which the event passes.

How?

• Composes effectiveSampleRate with the global telemetrySampleRate for:

  • Configuration telemetry events, with "configuration telemetry sample rate" of 20%.
  • Metrics telemetry events, with "metrics telemetry sample rate" of 15%.
  • Individual metrics events, like debug and error events.

• Logic centralized on SampleRate type alias:

  • Standard type for sample rate parameters
  • Logic for the composition of sample rates centralized in one place

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference
• Add CHANGELOG entry for user facing changes
• Add Objective-C interface for public APIs (see our guidelines [internal]) and run make api-surface)

[datadog-datadog-prod-us1]

Datadog Report

Branch report: simaoseica/RUM-6850/add-effective-sample-rate-to-telemetry-events
Commit report: 813cfcc
Test service: dd-sdk-ios

✅ 0 Failed, 3583 Passed, 0 Skipped, 2m 31.9s Total Time
🔻 Test Sessions change in coverage: 7 decreased, 5 increased, 2 no change

🔻 Code Coverage Decreases vs Default Branch (7)

This report shows up to 5 code coverage decreases.

• test DatadogSessionReplayTests iOS 34.28% (-0.08%) - Details
• test DatadogTraceTests tvOS 54.21% (-0.03%) - Details
• test DatadogLogsTests iOS 47.67% (-0.03%) - Details
• test DatadogLogsTests tvOS 47.73% (-0.03%) - Details
• test DatadogCrashReportingTests tvOS 26.66% (-0.02%) - Details

[ncreated]

🏅 🎯 Well done, LG!