Sign packages

[didierofrivia]

Is your feature request related to a problem? Please describe.
Currently our chart packages are not signed. Which means we can't guarantee the integrity of those to the users.

Describe the solution you'd like
Signing every package when it's created at their original repositories (authorino-operator, limitador-operator, dns-operator and kuadrant-operator) thus we not only will be guarantee the package integrity but also gaining the Signed badge at ArtifactsHub.io.

Notes
Here's a guide:
https://blog.devops.dev/a-guide-to-signing-helm-charts-with-gpg-using-github-action-and-sign-images-on-artifacthub-958a23010e94