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/plugin_key_value.go

@@ -0,0 +1,33 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+import (
+	"net/http"
+	"unicode/utf8"
+)
+
+const (
+	KeyValuePluginIdMaxRunes = 190
+	KeyValueKeyMaxRunes      = 150
+)
+
+type PluginKeyValue struct {
+	PluginId string `json:"plugin_id"`
+	Key      string `json:"key" db:"PKey"`
+	Value    []byte `json:"value" db:"PValue"`
+	ExpireAt int64  `json:"expire_at"`
+}
+
+func (kv *PluginKeyValue) IsValid() *AppError {
+	if kv.PluginId == "" || utf8.RuneCountInString(kv.PluginId) > KeyValuePluginIdMaxRunes {
+		return NewAppError("PluginKeyValue.IsValid", "model.plugin_key_value.is_valid.plugin_id.app_error", map[string]any{"Max": KeyValueKeyMaxRunes, "Min": 0}, "key="+kv.Key, http.StatusBadRequest)
+	}
+
+	if kv.Key == "" || utf8.RuneCountInString(kv.Key) > KeyValueKeyMaxRunes {
+		return NewAppError("PluginKeyValue.IsValid", "model.plugin_key_value.is_valid.key.app_error", map[string]any{"Max": KeyValueKeyMaxRunes, "Min": 0}, "key="+kv.Key, http.StatusBadRequest)
+	}
+
+	return nil
+}