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_valid.go

@@ -0,0 +1,40 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+import (
+	"regexp"
+	"unicode/utf8"
+)
+
+const (
+	MinIdLength  = 3
+	MaxIdLength  = 190
+	ValidIdRegex = `^[a-zA-Z0-9-_\.]+$`
+)
+
+// ValidId constrains the set of valid plugin identifiers:
+//
+//	^[a-zA-Z0-9-_\.]+
+var validId *regexp.Regexp
+
+func init() {
+	validId = regexp.MustCompile(ValidIdRegex)
+}
+
+// IsValidPluginId verifies that the plugin id has a minimum length of 3, maximum length of 190, and
+// contains only alphanumeric characters, dashes, underscores and periods.
+//
+// These constraints are necessary since the plugin id is used as part of a filesystem path.
+func IsValidPluginId(id string) bool {
+	if utf8.RuneCountInString(id) < MinIdLength {
+		return false
+	}
+
+	if utf8.RuneCountInString(id) > MaxIdLength {
+		return false
+	}
+
+	return validId.MatchString(id)
+}