setopt: add page

[gsspdev]

Checklist

• The page(s) are in the correct platform directories: common, linux, osx, windows, sunos, android, etc.
• The page description(s) have links to documentation or a homepage.
• The page(s) follow the content guidelines.
• The page(s) follow the style guide.
• The PR contains at most 5 new pages.
• The PR is authored by me, or has been human-reviewed if it was created with AI or machine translation software.
• The PR title conforms to the recommended templates.
• Version of the command being documented (if known):
• Reference issue: #

[msaf9]

Please resolve the build failure so that we can begin the actual review process.

[msaf9]

Hello @gsspdev, could you please fix the build failure and address one of the comments from the review?

[znarfm]

Since there will be a page for unsetopt in #19686, I think these suggestions should be applied.

[kbdharun]

LGTM, thanks for your contribution.