feat: install Flux V2 components

[TineoC]

This PR installs Flux V2 in the cfp-sandbox-cluster.

Required for: #123
Required for: CodeForPhilly/balancer-main#455

Changes:

1. flux-system/gotk-components.yaml: Contains the base Flux V2 components, including:
   • Source Controller
   • Kustomize Controller
   • Helm Controller
   • Notification Controller
   • Image Reflector Controller (Required for image automation)
   • Image Automation Controller (Required for image automation)
2. flux-system/gotk-sync.yaml: Configures Flux to sync with this repository (ssh://git@github.com/CodeForPhilly/cfp-sandbox-cluster) on the main branch.
3. flux-system/kustomization.yaml: Kustomize base for the Flux system.

Post-Install Steps:

After merging this PR, the following steps are required to complete the installation:

1. Apply the flux-system directory manually once: kubectl apply -k flux-system/
2. Configure the SSH secret for Git access (if using SSH) or ensure the cluster has access to the repository.
3. Verify the installation: flux check

[themightychris]

We evaluated this approach early on and rejected it in favor of a more "solid-state" GitHub-mediated approach with less moving parts. You can automate in GitHub actions from the balancer repo opening version bump PRs against CfP's sandbox and/or live clusters if you want to streamline things. Any cluster admin can see those PRs open in the Slack channel and approve them pretty quickly if they're just simple version bumps, but we want to let project repos define their own helm/k8s manifests too to allow version bumps to include more complex infrastructure changes as needed and to keep that locus of review/approval at the environment level

I appreciate that you put a lot of work into this and feel bad rejecting it, but in the future you really ought to open an issue for discussion first before jumping into major changes to the shared infrastructure