Add trailing slash toggle

[alex-plosceac]

Problem
Currently, there's no way to control whether documentation URLs end with a trailing slash (e.g., /docs/platform vs /docs/platform/). This can cause issues with SEO (duplicate content), analytics tracking, and consistency when integrating with platforms that enforce a specific URL convention.

Proposed solution
Add a configuration option (e.g., trailingSlash: true | false) that lets users choose whether generated URLs include a trailing slash. The setting should also handle redirects so both formats don't resolve simultaneously.

Use case
Our existing site enforces trailing slashes across all routes. When we migrated docs to Mintlify, the mismatch broke incoming links and split our search engine indexing across two URL variants.