[Registry] Specify header values as a list

What does this MR do?

Specifies header values as a list for registry notification entries, matching the expectation from the documentation: https://gitlab.com/gitlab-org/container-registry/-/blob/master/docs/configuration.md#endpoints

"A list of static headers to add to each request. Each header's name is a key beneath headers, and each value is a list of payloads for that header name. Values must always be lists."

Related issues

#2671 (closed)

Testing instructions

Create required secrets

kubectl create secret generic gitlab-registry-database-password --from-literal=password=randomstring
kubectl create secret generic gitlab-registry-authorization-header-v1 --from-literal=secret=randomstring

Install chart

Snippet below is for kind, but kind is not required here:

helm upgrade --install --set certmanager-issuer.email=no@no.com gitlab . -n default -f examples/registry/database-defaults.yaml -f examples/registry/notification.yaml -f examples/kind/values-base.yaml -f examples/kind/values-ssl.yaml --set global.hosts.domain=$(ipconfig getifaddr en0).nip.io

Create database for registry

https://gitlab.com/gitlab-org/charts/gitlab/blob/2671-registry-migation-config/doc/charts/registry/index.md#creating-the-database

Check logs

Check the logs in the registry pod to confirm that it started correctly without any errors.

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened

Closes #2671 (closed)