Test new `Bundle` with existing eks-a releases

When a new `Bundle` is created, we should test it with all the CLI versions that will use it. For new eks-a cli versions, that is already tested during the cli release. However, what about when we release a new `Bundle` for existing CLI versions?

We can use the staging pipelines for this purpose. We should have a different release manifest for staging. That means than when we create a new bundle in staging, we can actually modify the staging release manifest to make the latest release (or as many releases as we want) to point to this new bundle. If we then run the E2E tests with those CLI versions, they will use the new `Bundle`.

- [ ] #323
- [ ] #325

We might not need #325 if we follow the proposed design, since we already have tests that create clusters with a previous CLI and upgrade with the "current" one. Depending how this is configured for new `Bundle` tests, this might be enough. But leaving up to the implementer judgement to decide if we need extra test cases or not. We just need to make sure that clusters created with the current `Bundle` can be upgraded to the new one without issues.

Start by reading the staging pipelines and their release-manifest configuration, then trace how a staged Bundle is selected by existing CLI versions. Update the staging setup and run the relevant E2E upgrade scenarios; done means clusters created with the current Bundle can upgrade to the new Bundle across the selected CLI releases.

Written by the indexing model from the issue text.