Prepare for Flux v2.0.0-rc.1

[stefanprodan]

The fist release candidate of Flux GA comes with the promotion of the bootstrap related APIs to v1 and adds horizontal scaling & sharding capabilities to Flux controllers. In addition, this prerelease comes with support for auth with Azure Workload Identity.

TODOs:

• GA: Promote GitRepository to source.toolkit.fluxcd.io/v1 source-controller#947
• GA: Promote Kustomization to kustomize.toolkit.fluxcd.io/v1 kustomize-controller#755
• GA: Promote Receiver to notification.toolkit.fluxcd.io/v1 notification-controller#436
• Add controller sharding capability based on label selector #3731
• Make all project controllers private #3719
• Support Azure Workload Identity source-controller#1048
• Support Workload Identity for Azure Vault kustomize-controller#813
• Add PersistentClient flag to allow control over Kubernetes client behavior helm-controller#659
• controllers: update status patch logic helm-controller#660
• flux build and flux diff don't honor .sourceignore files #3695
• Add /v2 suffix to module name in preparation of 2.0.0 release #3737
• Mark non-bootstrap commands as "in preview and under development" #3739
• Implement --deploy-token-auth in GitLab bootstrapping #3654
• Update dependencies and GitRepository to v1 source-watcher#52
• Release Flux v2.0.0-rc.1 #3758

Release checklist:

• source-controller v1.0.0-rc.1
• kustomize-controller v1.0.0-rc.1
• notification-controller v1.0.0-rc.1
• helm-controller: v0.32.0
• image-reflector-controller v0.27.0
• image-automation-controller v0.32.0
• flux2 v2.0.0-rc.1
• terraform-provider-flux v1.0.0-rc.1
• source-watcher v1.0.0-rc.1

Documentation updates:

• Update GA Roadmap website#1453
• Add the sharding flag to controller docs
• Document how to configure sharding
• Update the API spec docs to v1
• Update all docs pages to v1
• Publish Flux release change log to GitHub & Slack