docs: Update link to turn on and off beta features

Description

Summary

This change fixes a broken documentation link in two places. The URL pointing to the "beta and experimental features" page was updated by removing the .md file extension from the link, which is the correct format for web-based documentation URLs.

Related issues and merge requests

• gitlab-org/technical-writing/team-tasks#1683 (closed)

Documentation

If this MR adds or updates CLI command documentation, follow the conventions in the GitLab CLI (glab) documentation style guide, run make gen-docs, and commit the updated files in docs/source/.