feat: watch mode with config

[sidnz]

This pull request introduces a new "watch" command to the Sentinel CLI, enabling continuous monitoring of targets with periodic scans and change detection. The implementation includes the command itself, updates to the documentation, and comprehensive integration tests to ensure correct behavior under various scenarios.

New Watch Command Functionality:

• Added a watch command to the CLI, allowing users to continuously monitor configuration files, endpoints, or containers, with options for scan interval, output format, change detection, and safe mode. The command handles graceful shutdown via SIGINT and supports reporting only on changes. (sentinel/cli.py)

Documentation Updates:

• Updated the CLI documentation to reflect the new fifth command (watch) and described its usage and options in the README.md file, including examples. (README.md) [1] [2]
• Updated the CLI docstring to mention the new "watch" command. (sentinel/cli.py)

Testing Enhancements:

• Added a comprehensive test class for the watch command, including fixtures to simulate single and multiple scan cycles, tests for output correctness, change detection, and output file writing. (tests/integration/test_cli.py)
• Included necessary imports for patching and signal handling in the test suite. (tests/integration/test_cli.py)