OS: Add generic OS command

[Asartea]

DO NOT MERGE: Depends on TheOdinProject/curriculum/pull/25402

Because

• Once we've moved to support WSL, its easier to disclaim that every OS not mentioned isn't supported, rather than trying to account for every possible edgecase (But what about TempleOS???)

This PR

• Adds a generic !os command which makes it clear that everything not mentioned as supported is unsupported

Pull Request Requirements

• I have thoroughly read and understand The Odin Project Contributing Guide
• The title of this PR follows the location of change: brief description of change format, e.g. Callbacks command: Update verbiage
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If this PR adds new features or functionality, I have added new tests
• If applicable, I have ensured all tests related to any command files included in this PR pass, and/or all snapshots are up to date