feat: Instrumentation

[tusharpandey13]

This change adds configurable instrumentation support to the SDK, enabling emitting events at various critical points of the SDK flows.
These events can be consumed using a callback.

Some use-cases for this feature:

• Event logging
• Debugging
• Event streaming and reactive workflows

Changes

Instrumentation infra:
These changes enable the actual instrumentation support.

• instrumentation-emitter.ts: InstrumentationEmitter class, helper methods
• instrumentation.flow.test.ts‎ & instrumentation.test.ts‎ : Tests
• types/instrumentation.ts: Type definitions
• EXAMPLES.md: Documentation

Event call sites:
These changes add call sites to existing SDK code at important points. PII data is not sent to emitter from codebase itself, removing the need for a filteration step.

• auth-client.ts: Most of the SDK flows
• client.ts: Configuration, one call site

Usage

1. Option1: Environment Variables

AUTH0_LOGGING_TARGET=console
AUTH0_LOGGING_LEVEL=info

Option 2: Custom callback

Configure a callback in Auth0ClientOptions:

export const auth0 = new Auth0Client({
  instrumentation: {
    logger: (event) => {
      // do what you want with the event here
      console.log(`[${event.level}] ${event.event}`, event.data);
    },
  },
});

Tests

Added unit and flow tests for complete integration.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.87%. Comparing base (6e9f186) to head (d306944).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2527      +/-   ##
==========================================
+ Coverage   90.50%   90.87%   +0.37%     
==========================================
  Files          52       54       +2     
  Lines        6632     6901     +269     
  Branches     1380     1421      +41     
==========================================
+ Hits         6002     6271     +269     
  Misses        619      619              
  Partials       11       11              

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