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/preference_test.go

@@ -0,0 +1,67 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestPreferenceIsValid(t *testing.T) {
+	preference := Preference{
+		UserId:   "1234garbage",
+		Category: PreferenceCategoryDirectChannelShow,
+		Name:     NewId(),
+	}
+
+	require.NotNil(t, preference.IsValid())
+
+	preference.UserId = NewId()
+	require.Nil(t, preference.IsValid())
+
+	preference.Category = strings.Repeat("01234567890", 20)
+	require.NotNil(t, preference.IsValid())
+
+	preference.Category = PreferenceCategoryDirectChannelShow
+	require.Nil(t, preference.IsValid())
+
+	preference.Name = strings.Repeat("01234567890", 20)
+	require.NotNil(t, preference.IsValid())
+
+	preference.Name = NewId()
+	require.Nil(t, preference.IsValid())
+
+	preference.Value = strings.Repeat("01234567890", 201)
+	require.NotNil(t, preference.IsValid())
+
+	preference.Value = "1234garbage"
+	require.Nil(t, preference.IsValid())
+
+	preference.Category = PreferenceCategoryTheme
+	require.NotNil(t, preference.IsValid())
+
+	preference.Value = `{"color": "#ff0000", "color2": "#faf"}`
+	require.Nil(t, preference.IsValid())
+}
+
+func TestPreferencePreUpdate(t *testing.T) {
+	preference := Preference{
+		Category: PreferenceCategoryTheme,
+		Value:    `{"color": "#ff0000", "color2": "#faf", "codeTheme": "github", "invalid": "invalid"}`,
+	}
+
+	preference.PreUpdate()
+
+	var props map[string]string
+	require.NoError(t, json.NewDecoder(strings.NewReader(preference.Value)).Decode(&props))
+
+	require.Equal(t, "#ff0000", props["color"], "shouldn't have changed valid props")
+	require.Equal(t, "#faf", props["color2"], "shouldn't have changed valid props")
+	require.Equal(t, "github", props["codeTheme"], "shouldn't have changed valid props")
+
+	require.NotEqual(t, "invalid", props["invalid"], "should have changed invalid prop")
+}