Prepare for v0.40 release

[stefanprodan]

The 0.40 release promotes the ImageRepository and ImagePolicy APIs to v1beta2 and deprecates the auto-login controller flags.

The GitRepository API has a new optional field .spec.ref.name that allows specifying a Git Reference. This allows Flux to reconcile resources from GitHub Pull Requests (refs/pull/<id>/head) and GitLab Merge Requests (refs/merge-requests/<id>/head). In addition, the source revision format changes as described by RFC-0005.

The OCI artifacts produced with flux push artifact have now custom media types:

• artifact media type application/vnd.oci.image.manifest.v1+json
• config media type application/vnd.cncf.flux.config.v1+json
• content media type application/vnd.cncf.flux.content.v1.tar+gzip

TODOs:

• Refactor reconcilers and introduce v1beta2 API image-reflector-controller#311
• add support for checking out to Git refs source-controller#1026
• RFC-0003: Introduce Flux OCI media type #3575
• git: change Commit#String format pkg#404
• RFC-0005: introduction of Digest and change of Revision format source-controller#1001
• Apply default permission mode to all files/dirs in an artifact archive  source-controller#1020
• rbac: Add view and edit aggregated cluster roles #3566
• Add flux stats command to print the reconcilers status #3578

Release checklist:

• source-controller v0.35.0
• kustomize-controller v0.34.0
• notification-controller v0.32.0
• helm-controller: v0.30.0
• image-automation-controller v0.30.0
• image-reflector-controller v0.25.0
• flux2 v0.40.0
• terraform-provider-flux v0.24.0

Documentation updates:

• image-reflector-controller v1beta2 updates website#1374
• Remove image reflector deprecated options website#1373
• security: Add view, edit and admin roles to RBAC docs website#1383
• Update the revision format in all guides: Update revision fmts to match RFC-0005 website#1384
• Publish Flux release change log to GitHub & Slack