Add pkg/cicd Deployer interface and Github implementation

[IsaacJames]

Introduces a new pkg/cicd package that provides a generic interface for triggering deployments via external CICD systems. This package will be used by the rollback controller to trigger rollback deployments and poll for their completion status.

Implementation

pkg/cicd/deployer.go

Core interface and types:

• Deployer interface:
  • TriggerDeployment(ctx, req) - Initiates a deployment in the CICD system
  • GetDeploymentStatus(ctx, deploymentID) - Retrieves current deployment status
  • Name() - Returns a human-readable deployer name for logging/metrics
• DeploymentRequest - Embeds Rollback and Release resources with provider-specific options
• DeploymentResult - Contains deployment ID, status, message, and URL
• DeploymentStatus - Enum for Pending, InProgress, Succeeded, Failed, Unknown
• DeployerError - Wraps errors with retryability information
• NoopDeployer - Test implementation that always succeeds immediately

pkg/cicd/github/deployer.go

GitHub Deployments API implementation:

• Derives owner/repo from the release's github type revision
• Supports multiple github revisions via the repository option
• Uses the deployment URL as the ID (encodes owner/repo/id for status polling)
• Marks 5xx and 429 errors as retryable

pkg/cicd/github/deployer_test.go

Unit tests covering deployment triggering, status polling, error handling, and helper functions

[goelozev]

Great job on the implementation!

I don't have any comments or suggestions as of now! Let me know when it's ready for another look!