v8.0 module release (#22975)

https://mattermost.atlassian.net/browse/MM-52079

```release-note
We upgrade the module version to 8.0. The new module path is github.com/mattermost-server/server/v8.
```


Co-authored-by: Doug Lauder <wiggin77@warpmail.net>

server/model/client4_test.go

@@ -0,0 +1,106 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// https://github.com/mattermost/mattermost-plugin-starter-template/issues/115
+func TestClient4TrimTrailingSlash(t *testing.T) {
+	slashes := []int{0, 1, 5}
+	baseURL := "https://foo.com:1234"
+
+	for _, s := range slashes {
+		testURL := baseURL + strings.Repeat("/", s)
+		client := NewAPIv4Client(testURL)
+		assert.Equal(t, baseURL, client.URL)
+		assert.Equal(t, baseURL+APIURLSuffix, client.APIURL)
+	}
+}
+
+// https://github.com/mattermost/mattermost-server/server/v8/channels/issues/8205
+func TestClient4CreatePost(t *testing.T) {
+	post := &Post{
+		Props: map[string]any{
+			"attachments": []*SlackAttachment{
+				{
+					Actions: []*PostAction{
+						{
+							Integration: &PostActionIntegration{
+								Context: map[string]any{
+									"foo": "bar",
+								},
+								URL: "http://foo.com",
+							},
+							Name: "Foo",
+						},
+					},
+				},
+			},
+		},
+	}
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var post Post
+		err := json.NewDecoder(r.Body).Decode(&post)
+		assert.NoError(t, err)
+		attachments := post.Attachments()
+		assert.Equal(t, []*SlackAttachment{
+			{
+				Actions: []*PostAction{
+					{
+						Integration: &PostActionIntegration{
+							Context: map[string]any{
+								"foo": "bar",
+							},
+							URL: "http://foo.com",
+						},
+						Name: "Foo",
+					},
+				},
+			},
+		}, attachments)
+		err = json.NewEncoder(w).Encode(&post)
+		assert.NoError(t, err)
+	}))
+
+	client := NewAPIv4Client(server.URL)
+	_, resp, err := client.CreatePost(post)
+	assert.NoError(t, err)
+	assert.Equal(t, http.StatusOK, resp.StatusCode)
+}
+
+func TestClient4SetToken(t *testing.T) {
+	expected := NewId()
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		authHeader := r.Header.Get(HeaderAuth)
+
+		token := strings.Split(authHeader, HeaderBearer)
+
+		if len(token) < 2 {
+			t.Errorf("wrong authorization header format, got %s, expected: %s %s", authHeader, HeaderBearer, expected)
+		}
+
+		assert.Equal(t, expected, strings.TrimSpace(token[1]))
+
+		var user User
+		err := json.NewEncoder(w).Encode(&user)
+		assert.NoError(t, err)
+	}))
+
+	client := NewAPIv4Client(server.URL)
+	client.SetToken(expected)
+
+	_, resp, err := client.GetMe("")
+	assert.NoError(t, err)
+	assert.Equal(t, http.StatusOK, resp.StatusCode)
+}