Modernize structured logging and redact HTTP request/response logs #1337

Summary

Modernize Shared.Logger and HTTP request/response logging in Shared.Middleware to emit structured, correlation-friendly events while reducing the risk of logging sensitive data.

Changes

Shared.Logger

• Add message-template overloads with arguments across log levels, including exception-aware error and critical logging.
• Emit NLog events with structured properties for event ID, UTC timestamp, service name, severity, tenant and merchant IDs, correlation ID, and distributed trace/span IDs when available.
• Keep existing message-only APIs available with obsolescence guidance, and remove the Microsoft.Extensions.Logging adapter in favor of the NLog implementation.
• Add a sample project demonstrating logger configuration and use.

Shared.Middleware

• Emit structured HTTP request and response events with request ID, method/path/query, status code, elapsed time, headers, body capture status, and health-check classification.
• Redact configured sensitive query, header, JSON, form, and XML values; filter headers through configurable allowlists.
• Bound request and response body capture by configurable byte limits and report unsupported, oversized, or failed captures without logging the body.
• Preserve request/response stream behavior and classify health-check paths case-insensitively.

Acceptance criteria

• Logger events retain message-template arguments and include available tenant, correlation, and trace context.
• Middleware logs only allowlisted headers and redacts configured sensitive values in supported body formats and query parameters.
• Body capture limits and capture-status outcomes are configurable and represented in structured events.
• The sample project demonstrates the updated logger API.