Release pipeline: implement CDN cache invalidation for non-versioned files

Implement programmatic cache purge for non-versioned files under `public/cli/v5/` (version.json, install scripts) as part of the release CI pipeline. Versioned artifact folders (`{version}/`) are immutable and should not be purged.

Investigate CDN API for programmatic cache drop.

Related: #5333, #5422

Start by locating the release CI pipeline that publishes files under public/cli/v5/ and identify the CDN provider and its cache-invalidation API. The work is done when the pipeline purges non-versioned files such as version.json and install scripts while leaving versioned artifact folders immutable.

Written by the indexing model from the issue text.