Fix image name parsing with tag and digest (#4406)

* Fix image name parsing with name and digest

Image names may contain both tag name and digest.  For example
`nginx:1.21.5@sha256:7826426c9d8d310c62fc68bcd5e8dde70cb39d4fbbd30eda3b1bd03e35fbde29`. Kustomizations with image transforms will not match
these image because the image parser assumes either a tag or digest, but not
both.

For a real life example of kuberenetes deployments that might need to perform
these types of transforms is from the [tekton-pipelines](https://github.com/tektoncd/pipeline) project (see the release.yaml).

* Return digest property from image name parser

image.Split now returns 3 fields: name, tag, and digest. The tag and digest
fields no longer include their respective delimiters (`:` and `@`).

* Fix merge file indentation

* Refactor imagetag updater string builder

api/image/image_test.go

@@ -23,11 +23,23 @@ func TestIsImageMatched(t *testing.T) {
 			isMatched: true,
 		},
 		{
-			testName:  "name is match",
+			testName:  "name is match with tag",
 			value:     "nginx:12345",
 			name:      "nginx",
 			isMatched: true,
 		},
+		{
+			testName:  "name is match with digest",
+			value:     "nginx@sha256:xyz",
+			name:      "nginx",
+			isMatched: true,
+		},
+		{
+			testName:  "name is match with tag and digest",
+			value:     "nginx:12345@sha256:xyz",
+			name:      "nginx",
+			isMatched: true,
+		},
 		{
 			testName:  "name is not a match",
 			value:     "apache:12345",
@@ -49,32 +61,65 @@ func TestSplit(t *testing.T) {
 		value    string
 		name     string
 		tag      string
+		digest   string
 	}{
 		{
 			testName: "no tag",
 			value:    "nginx",
 			name:     "nginx",
 			tag:      "",
+			digest:   "",
 		},
 		{
 			testName: "with tag",
 			value:    "nginx:1.2.3",
 			name:     "nginx",
-			tag:      ":1.2.3",
+			tag:      "1.2.3",
+			digest:   "",
 		},
 		{
 			testName: "with digest",
-			value:    "nginx@12345",
+			value:    "nginx@sha256:12345",
 			name:     "nginx",
-			tag:      "@12345",
+			tag:      "",
+			digest:   "sha256:12345",
+		},
+		{
+			testName: "with tag and digest",
+			value:    "nginx:1.2.3@sha256:12345",
+			name:     "nginx",
+			tag:      "1.2.3",
+			digest:   "sha256:12345",
+		},
+		{
+			testName: "with domain",
+			value:    "docker.io/nginx:1.2.3",
+			name:     "docker.io/nginx",
+			tag:      "1.2.3",
+			digest:   "",
+		},
+		{
+			testName: "with domain and port",
+			value:    "foo.com:443/nginx:1.2.3",
+			name:     "foo.com:443/nginx",
+			tag:      "1.2.3",
+			digest:   "",
+		},
+		{
+			testName: "with domain, port, tag and digest",
+			value:    "foo.com:443/nginx:1.2.3@sha256:12345",
+			name:     "foo.com:443/nginx",
+			tag:      "1.2.3",
+			digest:   "sha256:12345",
 		},
 	}
 
 	for _, tc := range testCases {
 		t.Run(tc.testName, func(t *testing.T) {
-			name, tag := Split(tc.value)
+			name, tag, digest := Split(tc.value)
 			assert.Equal(t, tc.name, name)
 			assert.Equal(t, tc.tag, tag)
+			assert.Equal(t, tc.digest, digest)
 		})
 	}
 }