feat: support latest-only releases

[richcooper95]

Changes:

• Hard-code v0.0.0-latest as the Kratix chart version (needs to be semver-ish!)
• Update the GH Action to set skip_existing to false

[richcooper95]

TODO:

• Investigate how the Helm Chart Releaser deals with a release/tag of the same name (kratix-v0.0.0-latest) already existing
• Test that we can deploy this change and see the updated Kratix manifest

It looks like the Helm Chart Releaser generates a new GH release, which creates a new tag of that release name. This was fine when every release name was unique (versioned), but may cause issues when we are always using the same release/tag name.

We might need to delete the old release/tag before regenerating them with the Helm Chart Releaser.

[richcooper95]

• Also check the index.yaml in the gh-pages branch, and whether the created timestamp gets updated when the version doesn't change (suspicion: yes)