Deprecate arch flags in favor of multi-arch images

This commit deprecates the architecture flag (`--arch`) for the install
and bootstrap commands, in favor of the bundled multi-arch images that
will be available for the next MINOR range of GOTK controller releases.

Summary of changes:

* `*Arch` variables have been marked as deprecated for both commands.
* `-arm64` suffix is no longer selectively added to the image definition
  of a component's `Deployment`.
* `kubernetes.io/arch` node selector with the defined value has been
  removed from the components' `Deployment`s.
* `Arch` has been removed from the available `Options` in
  `manifestgen/install`.
* Documentation references have been changed to highlight existence
  of multi-arch images and supported architectures.

Signed-off-by: Hidde Beydals <hello@hidde.co>

pkg/manifestgen/install/templates.go

@@ -28,7 +28,6 @@ var kustomizationTmpl = `---
 {{- $eventsAddr := .EventsAddr }}
 {{- $watchAllNamespaces := .WatchAllNamespaces }}
 {{- $registry := .Registry }}
-{{- $arch := .Arch }}
 {{- $logLevel := .LogLevel }}
 {{- $clusterDomain := .ClusterDomain }}
 apiVersion: kustomize.config.k8s.io/v1beta1
@@ -110,11 +109,7 @@ patchesJson6902:
 images:
 {{- range $i, $component := .Components }}
   - name: fluxcd/{{$component}}
-{{- if eq $arch "amd64" }}
     newName: {{$registry}}/{{$component}}
-{{- else }}
-    newName: {{$registry}}/{{$component}}-arm64
-{{- end }}
 {{- end }}
 {{- end }}
 `
@@ -136,7 +131,6 @@ spec:
   template:
     spec:
       nodeSelector:
-        kubernetes.io/arch: {{.Arch}}
         kubernetes.io/os: linux
 {{- if .ImagePullSecret }}
       imagePullSecrets: