[FEATURE] Encina.GoogleCloudPubSub - Google Cloud Pub/Sub transport

[dlrivada]

Summary

Add Google Cloud Pub/Sub as a message transport to complete the cloud provider triangle (AWS, Azure, GCP).

Motivation

• GCP is one of the three major cloud providers
• Many enterprises use GCP for their infrastructure
• Pub/Sub offers dead-letter queues, filtering, and horizontal scalability similar to Azure Service Bus
• Completes Encina's cloud-native story

Proposed Solution

New Package

• Encina.GoogleCloudPubSub

Interfaces

• IGoogleCloudPubSubMessagePublisher
• Integration with Google.Cloud.PubSub.V1 SDK

Features

• Topic/Subscription model
• Message ordering (ordering keys)
• Dead-letter topics
• Message filtering
• Exactly-once delivery
• Push and pull subscriptions

Configuration

services.AddEncinaGoogleCloudPubSub(options =>
{
    options.ProjectId = "my-project";
    options.TopicId = "my-topic";
    options.SubscriptionId = "my-subscription";
});

Alternatives Considered

1. AWS/Azure only: Supporting only AWS and Azure cloud providers. This excludes GCP users.

2. Generic HTTP API: Using a generic HTTP publisher instead of native SDK. This loses GCP-specific features and optimizations.

3. Dapr for GCP: Using Dapr with GCP Pub/Sub component. This adds Dapr dependency for simple GCP scenarios.

Affected Packages

• Encina (core)
• Encina.AspNetCore
• Encina.EntityFrameworkCore
• Encina.Dapper.*
• Encina.ADO.*
• Encina.MongoDB
• Encina.Messaging
• Encina.Caching.*
• Other: Encina.GoogleCloudPubSub

Additional Context

Implementation Tasks

• Create Encina.GoogleCloudPubSub package
• Implement publisher
• Implement consumer/subscriber
• Message ordering support
• Dead-letter topic handling
• Message filtering
• Health check integration
• OpenTelemetry traces/metrics
• Unit tests
• Integration tests with emulator

References

• Google Cloud Pub/Sub Documentation
• .NET Client Library

Acceptance Criteria

• Publisher implementation
• Consumer/Subscriber implementation
• Message ordering support
• Dead-letter topic handling
• Health check integration
• OpenTelemetry traces/metrics
• Unit tests
• Integration tests with emulator

Related Issues

• Encina.AmazonSQS (existing)
• Encina.AzureServiceBus (existing)