Sign artifacts

[slashpai]

Chart

perses, perses-operator

Proposal

Currently artifact hub shows both charts as not signed. We need to sign the charts during release

Ref: https://helm.sh/docs/topics/provenance/

For OCI artifacts could use cosign for keyless signing with Sigstore

Ref: https://github.com/sigstore/cosign-installer

[slashpai]

cc @ibakshay