RUM-8042 Batch Blocked telemetry with generic aggregation

[maxep]

What and why?

Introduce a new telemetry metric for tracking batch upload issues. It replaces the previous "Upload Quality" telemetry with a more specific "Batch Blocked" metric that provides better visibility into upload failures. This change provides a telemetry format more suitable for graphing.

More context in RFC (internal)

How?

The implementation uses a generic metric telemetry aggregation to collect metric and report them when the application is pushed to background:

1. Metric Types:

• Counter metrics for tracking increments (e.g., number of blocked batches)
• Gauge metrics for tracking values (e.g., pending batches count)
• Custom metric events for specific metrics

2. Metrics:

• batch_blocked: Tracks the number of times batch uploads are blocked
• pending_batches: Tracks the number of batches waiting to be uploaded
• upload_cycle: Monitors count of upload cycle

Each metric supports configurable cardinalities for detailed analysis

4. Architecture:

• Generic aggregation system that can handle different metric types
• Flexible cardinality configuration for each metric
• Separation between metric collection and aggregation

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: maxep/RUM-8042/batch-blocked-telemetry
Commit report: 2cab83e
Test service: dd-sdk-ios

✅ 0 Failed, 2423 Passed, 1485 Skipped, 3m 5.28s Total duration (1m 11.75s time saved)

[mariedm]

LGMT!

[simaoseica-dd]

LGTM 👌

[barboraplasovska]

🏅

[mariedm]

Just a couple of small questions, otherwise LGMT!