/os: Amend title and body wording

[MaoShizhong]

Because

The current /os command has "Windows" as a title - a carryover from when it used to be /windows? The embed text could also probably do with being explicit about what Linux distros we do support.

This PR

• Amends /os command title to be OS-agnostic
• Amends /os embed wording and link text label
• Removes the url property from !os command to be consistent with other commands (not really used anyway since it just makes the title a link, and the embed already contains that link)
• Updates /os snapshots

Issue

N/A

Additional Information

Pull Request Requirements

• [x] I have thoroughly read and understand The Odin Project Contributing Guide
• [x] The title of this PR follows the location of change: brief description of change format, e.g. Callbacks command: Update verbiage
• [x] The Because section summarizes the reason for this PR
• [x] The This PR section has a bullet point list describing the changes in this PR
• [x] If this PR addresses an open issue, it is linked in the Issue section
• [x] If this PR adds new features or functionality, I have added new tests
• [x] 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