Add --dry-run flag to CLI (#1967)

[YUVRAJ-SINGH-3178]

Hey! This PR adds a handy --dry-run flag to the CLI as requested in #1967.

It makes it super easy to preview exactly what command a plugin is going to run under the hood, without actually firing off a scan or saving a task to the database.

Here's how it works:

• Added the --dry-run argument to the secuscan scan parser in cli.py.
• If the flag is passed, it uses the plugin_manager to build the command with all the interpolated inputs.
• It also fully simulates the Docker sandbox environment by prepending the exact docker run prefix (with memory/cpu limits) that the executor would normally use.
• Finally, it just prints the final resolved command to the terminal and cleanly exits with a 0 code.

It's great for debugging plugins. Let me know what you think!