[4.8] Sphinx theme: Redoc theme option

[vamera]

Description

This PR updates the version of Redoc used by our Sphinx theme and sets the theme attribute in the redoc tag.

Documentation compilation

• [x] Verified that documentation compiles without warnings.

Changelog

• [ ] Updated CHANGELOG.md.

Code formatting & web optimization

• [ ] Added or updated meta descriptions.
• [ ] Updated redirects.js if necessary (guide).
• [ ] Used three-space indentation in .rst files.

Writing style

• [ ] Used bold for UI elements, italics for key terms or emphasis, and code font for Bash commands, file names, REST paths, and code.
• [ ] Followed present tense, active voice, and a semi-formal tone.
• [ ] Wrote short, clear, and concise sentences.