Add Wire Tap feature for endpoint-level message auditing

[jeremydmiller]

Summary

• Implements the Wire Tap pattern from EIP for endpoint-level message auditing, compliance, and monitoring
• Adds IWireTap interface with RecordSuccessAsync(Envelope) and RecordFailureAsync(Envelope, Exception) methods
• Wire taps are configured per-endpoint via UseWireTap() fluent API on listeners, senders, and local queues
• Supports keyed DI services (UseWireTap("key")) to vary wire tap implementations across endpoints
• Can be applied in bulk via opts.Policies.AllListeners(), AllLocalQueues(), and AllSenders()
• Wire tap calls are wrapped in try/catch safety nets and fire-and-forget to stay off the hot path
• Includes documentation in the logging/auditing page with BatchingChannel recommendations

Closes #2222

Test plan

• Wire tap records success on message handled
• Wire tap not called when not configured on endpoint
• Wire tap not set on endpoint without configuration
• UseWireTap flag works correctly
• Default wire tap used without key
• Keyed wire tap used with service key

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