Migrate sourcesecret package to runtime/secrets APIs

The sourcesecret package now uses pkg/runtime/secrets factory
functions instead of the previous monolithic approach. This
provides standardized secret generation with consistent
validation and error handling across all authentication types.

Signed-off-by: cappyzawa <cappyzawa@gmail.com>

cmd/flux/testdata/create_secret/githubapp/secret-with-baseurl.yaml

@@ -36,4 +36,5 @@ stringData:
     lbD102oXw9lUefVI0McyQIN9J58ewDC79AG7gU/fTSt6F75OeFLOJmoedQo33Y+s
     bUytJtOhHbLRNxwgalhjBUNWICrDktqJmumNOEOOPBqVz7RGwUg=
     -----END RSA PRIVATE KEY-----
+type: Opaque
 

cmd/flux/testdata/create_secret/githubapp/secret.yaml

@@ -35,4 +35,5 @@ stringData:
     lbD102oXw9lUefVI0McyQIN9J58ewDC79AG7gU/fTSt6F75OeFLOJmoedQo33Y+s
     bUytJtOhHbLRNxwgalhjBUNWICrDktqJmumNOEOOPBqVz7RGwUg=
     -----END RSA PRIVATE KEY-----
+type: Opaque
 

cmd/flux/testdata/create_secret/helm/secret-helm.yaml

@@ -7,4 +7,5 @@ metadata:
 stringData:
   password: my-password
   username: my-username
+type: kubernetes.io/basic-auth
 

cmd/flux/testdata/create_secret/oci/create-secret.yaml

@@ -5,6 +5,15 @@ metadata:
   name: ghcr
   namespace: my-namespace
 stringData:
-  .dockerconfigjson: '{"auths":{"ghcr.io":{"username":"stefanprodan","password":"password","auth":"c3RlZmFucHJvZGFuOnBhc3N3b3Jk"}}}'
+  .dockerconfigjson: |-
+    {
+      "auths": {
+        "ghcr.io": {
+          "username": "stefanprodan",
+          "password": "password",
+          "auth": "c3RlZmFucHJvZGFuOnBhc3N3b3Jk"
+        }
+      }
+    }
 type: kubernetes.io/dockerconfigjson
 

cmd/flux/testdata/create_secret/proxy/secret-proxy.yaml

@@ -8,4 +8,5 @@ stringData:
   address: https://my-proxy.com
   password: my-password
   username: my-username
+type: Opaque