Add (create|delete|export) source chart commands

The `create source chart` command supports all HelmChart.spec fields
except `.valuesFiles` and `ignoreMissingValuesFiles` as these are
assumingly rarely used fields and the CLI usually only supports
commonly used ones.

closes #4760

Co-authored-by: Stefan Prodan <stefan.prodan@gmail.com>
Signed-off-by: Max Jonas Werner <mail@makk.es>

cmd/flux/testdata/create_source_chart/setup-source.yaml

@@ -0,0 +1,16 @@
+---
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: {{ .fluxns }}
+---
+apiVersion: source.toolkit.fluxcd.io/v1
+kind: HelmRepository
+metadata:
+  name: podinfo
+  namespace: {{ .fluxns }}
+spec:
+  interval: 1m0s
+  provider: generic
+  type: oci
+  url: oci://ghcr.io/stefanprodan/charts