Improve Open VSX development & deployment workflow

Currently, Open VSX site updates can get blocked for various reasons, slowing down feature delivery and creating bottlenecks. I’d like us to improve the development and deployment process to support parallel work and avoid relying on a single path to production.

As a concrete example, @amvanbaren has been working to add Redis support to our existing rate-limiting mechanism, but that work is currently blocked because the Redis instance isn’t ready for production. At the same time, we need to make changes to the Open VSX website to publish updates to the [Open VSX Publisher Agreement](https://gitlab.eclipse.org/eclipsefdn/helpdesk/-/issues/6622). However, since the Redis work is on staging, it’s blocking @amvanbaren from working on the changes needed to support the new Publisher Agreement.

I’ve asked him to make an exception and revert some of that work so we can finalize the Publisher Agreement update as soon as possible, but this is not ideal and creates additional work for everyone involved.

**Goals:**

- Establish a reliable and flexible **dev → staging → production** flow.
- Allow developers to work on multiple features and test them on staging without blocking other updates.
- Reduce the risk of being unable to update the site while work is in progress.

**Options to explore:**

- Support multiple staging environments so different feature branches can be tested at the same time.
- Alternatively, adjust the dev process to allow overriding the staging branch to test different features when needed.

**Proposed next steps:**

- Review the current deployment process with @fredg02 and @amvanbaren .
- Identify gaps that cause blocking or delays.
- Implement and document the new process.

/cc @agafgfafa @kineticsquid