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/plugin/checker/internal/test/invalid/invalid.go

@@ -0,0 +1,36 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package invalid
+
+type API interface {
+	// ValidMethod is a fake method for testing the
+	// plugin comment checker with a valid comment.
+	//
+	// Minimum server version: 1.2.3
+	ValidMethod()
+
+	// InvalidMethod is a fake method for testing the
+	// plugin comment checker with an invalid comment.
+	InvalidMethod()
+}
+
+type Helpers interface {
+	// Minimum server version: 1.1
+	LowerVersionMethod()
+
+	// Minimum server version: 1.3
+	HigherVersionMethod()
+}
+
+type HelpersImpl struct {
+	api API
+}
+
+func (h *HelpersImpl) LowerVersionMethod() {
+	h.api.ValidMethod()
+}
+
+func (h *HelpersImpl) HigherVersionMethod() {
+	h.api.ValidMethod()
+}

server/plugin/checker/internal/test/missing/missing.go

@@ -0,0 +1,8 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package missing
+
+// SomeType is a fake interface for testing the plugin comment checker.
+type SomeType interface {
+}

server/plugin/checker/internal/test/valid/valid.go

@@ -0,0 +1,44 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package valid
+
+type API interface {
+	// ValidMethod is a fake method for testing the
+	// plugin comment checker with a valid comment.
+	//
+	// Minimum server version: 1.2.3
+	ValidMethod()
+
+	// Minimum server version: 1.5
+	NewerValidMethod()
+}
+
+type Helpers interface {
+	// Minimum server version: 1.2.3
+	ValidHelperMethod()
+
+	// Minimum server version: 1.5
+	NewerValidHelperMethod()
+
+	// Minimum server version: 1.5
+	IndirectReferenceMethod()
+}
+
+type HelpersImpl struct {
+	api API
+}
+
+func (h *HelpersImpl) ValidHelperMethod() {
+	h.api.ValidMethod()
+}
+
+func (h *HelpersImpl) NewerValidHelperMethod() {
+	h.api.NewerValidMethod()
+	h.api.ValidMethod()
+}
+
+func (h *HelpersImpl) IndirectReferenceMethod() {
+	a := h.api
+	a.NewerValidMethod()
+}