Add worker commands to the CLI

[berggren]

Summary

Implemented a new CLI command group and subcommand to list registered workers from the system API.

Technical Details:

• Command Registration: Added newWorkersCmd to the root command structure in cmd/openrelik/internal/cli/cli.go, enabling workers as a top-level CLI category.
• Worker Listing Logic: Created newListWorkersCmd in cmd/openrelik/internal/cli/workers.go. This command interacts with the worker service via client.Workers().Registered() to fetch worker metadata and uses formatAndPrint for output rendering.
• API Integration: Configured the command to communicate with the /api/v1/taskqueue/tasks/registered endpoint.
• Testing: Added cmd/openrelik/internal/cli/workers_test.go containing unit tests that mock the API server. These tests verify correct command execution, output parsing, and support for JSON formatting via the --output flag.