Add CLI client

[berggren]

Summary

Initial OpenRelik command-line interface with support for authentication, configuration persistence, and user profile management.

A command line tool to interact with the OpenRelik API

Usage:
  openrelik [command]

Available Commands:
  auth        Manage authentication
  completion  Generate the autocompletion script for the specified shell
  help        Help about any command
  users       Manage users

Flags:
  -h, --help            help for openrelik
  -o, --output string   Output format (text, json) (default "text")
  -q, --quiet           Suppress all output

Use "openrelik [command] --help" for more information about a command.

Technical Details:

• CLI Architecture: Established the root command structure using the cobra library, including global flags for output formatting (--output) and a quiet mode (--quiet).
• Authentication System: Implemented an auth login command that prompts for the server URL and API key. It uses golang.org/x/term to mask sensitive input during the login process.
• Configuration Management: Created a persistence layer that stores settings and credentials in ~/.openrelik/. It features atomic file writes and enforces restricted file permissions (0600 for files, 0700 for directories) to protect sensitive data.
• Client Provider Logic: Developed a client initialization sequence that resolves server details and credentials by checking command-line flags, environment variables, and local configuration files in order of priority.
• User Operations: Added a users me command to fetch and display the authenticated user's profile information.
• Output Formatting: Built utility functions for standardized output, supporting both a reflection-based text table format and pretty-printed JSON.
• Testing Suite: Included unit and integration tests for the CLI commands, configuration logic, and utility functions, using a mock API server for command validation.