[FEAT] Add GCP Cloud Function support to Go template

[colbytimm]

Summary

The Go template currently only supports Azure Function App. Add GCP Cloud Function as a cloud_service option using the Go Functions Framework (github.com/GoogleCloudPlatform/functions-framework-go). Includes a Firestore repository using cloud.google.com/go/firestore.

Category: gcp, go

Acceptance Criteria

• cookiecutter.json includes "GCP Cloud Function" in cloud_service choices
• GCP entry point using github.com/GoogleCloudPlatform/functions-framework-go
• Firestore repository using cloud.google.com/go/firestore SDK implementing all CRUD operations
• go.mod conditionally includes GCP dependencies via Jinja2
• hooks/ directory with pre/post gen scripts for input validation and file cleanup
• Environment variables: GCP_PROJECT_ID, FIRESTORE_DATABASE, FIRESTORE_COLLECTION
• Unit tests pass for GCP variant with mocked Firestore client
• CI pipeline matrix includes GCP Cloud Function
• README updated with GCP-specific setup instructions

Implementation Notes

Go GCP Dependencies

• github.com/GoogleCloudPlatform/functions-framework-go (function hosting)
• cloud.google.com/go/firestore (Firestore client)
• google.golang.org/api (Google API core)

Key Files to Modify/Create

• go/cookiecutter.json — Add "GCP Cloud Function" to choices
• go/{{cookiecutter.project_class_name}}/repositories/repository.go — Add Jinja2 conditional for Firestore client
• go/{{cookiecutter.project_class_name}}/main.go — Add GCP entry point (Jinja2 conditional, separate from Azure custom handler)
• go/{{cookiecutter.project_class_name}}/go.mod — Conditional GCP dependencies
• go/hooks/pre_gen_project.py — Input validation (new)
• go/hooks/post_gen_project.py — Cloud-specific file cleanup (new)
• .github/workflows/build-go-pipeline.yaml — Add GCP Cloud Function to matrix
• Makefile — Add GCP-specific run command using functions-framework

GCP Cloud Function Entry Point Pattern (Go)

package function

import (
    "github.com/GoogleCloudPlatform/functions-framework-go/functions"
    "net/http"
)

func init() {
    functions.HTTP("GetList", getList)
    functions.HTTP("Get", get)
    // ... etc
}

Reference

Python and TypeScript templates already support GCP — follow their Jinja2 conditional patterns for consistency.