Implement controller for managing basic lifecycle of SSHServer

Summary

SSHServer controller is responsible for:

• Generating Secrets that are used internally or by other components, including GitLab Rails application, notably SSH host keys.
• Rendering GitLab Shell and OpenSSH configuration from specification.
• Provisioning workload and other managed resources for GitLab Shell.
• Reflecting the condition of resource with Status sub-resource and communicating its state using events.

Success criteria

The controller:

• Renders the configuration of GitLab Shell according to SSHServer specification.
• Configures and provisions the workload for GitLab Shell from SSHServer specification.
• Updates and communicates the state and condition of application deployment.
• Scales the application when kubectl scale command is used to scale the resource up or down.