Add flags for issuer/subject OCI signature verification

This change introduces two new flags to `create source oci` for
providing the values to the
`OCIRepository.spec.verify.matchOIDCIdentity.(issuer,subject)` fields.

Signed-off-by: Max Jonas Werner <mail@makk.es>

cmd/flux/testdata/oci/export_with_complete_verification.golden

@@ -0,0 +1,16 @@
+---
+apiVersion: source.toolkit.fluxcd.io/v1beta2
+kind: OCIRepository
+metadata:
+  name: podinfo
+  namespace: flux-system
+spec:
+  interval: 0s
+  ref:
+    tag: 6.3.5
+  url: oci://ghcr.io/stefanprodan/manifests/podinfo
+  verify:
+    matchOIDCIdentity:
+    - issuer: github
+      subject: stefanprodan
+    provider: cosign

cmd/flux/testdata/oci/export_with_issuer.golden

@@ -0,0 +1,16 @@
+---
+apiVersion: source.toolkit.fluxcd.io/v1beta2
+kind: OCIRepository
+metadata:
+  name: podinfo
+  namespace: flux-system
+spec:
+  interval: 0s
+  ref:
+    tag: 6.3.5
+  url: oci://ghcr.io/stefanprodan/manifests/podinfo
+  verify:
+    matchOIDCIdentity:
+    - issuer: github
+      subject: ""
+    provider: cosign

cmd/flux/testdata/oci/export_with_subject.golden

@@ -0,0 +1,16 @@
+---
+apiVersion: source.toolkit.fluxcd.io/v1beta2
+kind: OCIRepository
+metadata:
+  name: podinfo
+  namespace: flux-system
+spec:
+  interval: 0s
+  ref:
+    tag: 6.3.5
+  url: oci://ghcr.io/stefanprodan/manifests/podinfo
+  verify:
+    matchOIDCIdentity:
+    - issuer: ""
+      subject: stefanprodan
+    provider: cosign