Disable cache for _gen/docs-index.json

Hello,

Browsers save this file in cache, which causes problems. When we release a new version, the new version does not appear immediately for the version selection menu.

The easiest way to do this is to add a random text string to request HTTP. However, we can also try to implement it through .htaccess, or in two ways at the same time.

Best regards,
Kamil Breguła