feat: add CloudAMQP cost monitoring plugin

[demo112]

CloudAMQP Plugin for OpenCost

Implements a cost monitoring plugin for CloudAMQP managed RabbitMQ services.

What it does

• Fetches billing invoices from the CloudAMQP API
• Enriches cost data with instance metadata (region, plan, name)
• Supports configurable rate limiting for API calls
• Implements the CustomCostSource interface following the FOCUS spec
• Includes unit tests for core functionality

Plugin Structure

pkg/plugins/cloudamqp/
├── cmd/main/main.go          # Main plugin implementation
├── cmd/main/main_test.go     # Unit tests
├── cloudamqpplugin/config.go # Configuration handling
├── cloudamqpplugin/types.go  # API response types
├── go.mod / go.sum           # Module dependencies

Configuration

The plugin requires the following config values:

• cloudamqp_api_key: CloudAMQP API key
• cloudamqp_account_id: CloudAMQP account ID

Testing

cd pkg/plugins/cloudamqp
go test ./cmd/main/

Related Issue

Resolves #54

Bounty

This plugin qualifies for the OpenCost plugin bounty program ($1,000 per accepted plugin as documented at https://www.opencost.io/blog/introducing-opencost-plugins).