Update CertManager from 1.5.4 to 1.6.1

Summary

Updates CertManager from 1.5.4 to 1.6.1.

Changes

• Updates CertManager package version to 1.6.1
• Updates deprecated API references to v1
• Updates CertManager CRD manifests
• Updates CertManager version in scripts/install_certmanager.sh

References

• https://cert-manager.io/docs/release-notes/release-notes-1.6/
• https://cert-manager.io/docs/installation/upgrading/upgrading-1.5-1.6/
• https://cert-manager.io/docs/installation/upgrading/

Testing

CI

Full pipeline (CI running CertManager 1.1.0): https://gitlab.com/gitlab-org/cloud-native/gitlab-operator/-/pipelines/442114831

Manual testing:

1. Deploy CertManager 1.6.1:

   kubectl apply -f https://github.com/jetstack/cert-manager/releases/download/v1.6.1/cert-manager.yaml

2. Deploy Operator:

   TAG=435-update-certmanager make build_operator
   kubectl create ns gitlab-system
   kubectl apply -f .build/operator.yaml

3. Apply a GitLab CR:

   apiVersion: apps.gitlab.com/v1beta1
   kind: GitLab
   metadata:
     name: gitlab
   spec:
     chart:
       version: "5.6.0"
       values:
         global:
           hosts:
             domain: yourdomain.com
         certmanager-issuer:
           email: youremail@example.com

4. Validate that certificates are issued as expected.

Notes

• CI clusters are currently running CertManager 1.1.0, but all works as expected still so that's not a blocker. I created #521 (closed) to track updating CertManager to 1.6.x in CI clusters.

Closes #435 (closed)