Refactor: func StringInSlice to slices.Contains (#24262)

* Refactor: Use generic to change func StringInSlice to Contains

* Refactor: Use generic to change func stringNotInSlice to Contains

Make utils.go (dir server/public/utils) and func Contains

* Refactor: Move func Contains from channels/utils to public/utils

Move func Contains from channels/utils to public/utils

Fix import declarations line

* Docs: Add a description of the Contains function

* Test: add TestContains

Add a test code for a Contain function

server/channels/store/searchtest/testlib.go

@@ -6,8 +6,9 @@ package searchtest
 import (
 	"testing"
 
+	pUtils "github.com/mattermost/mattermost/server/public/utils"
+
 	"github.com/mattermost/mattermost/server/v8/channels/store"
-	"github.com/mattermost/mattermost/server/v8/channels/utils"
 )
 
 const (
@@ -35,12 +36,12 @@ type searchTest struct {
 func filterTestsByTag(tests []searchTest, tags ...string) []searchTest {
 	filteredTests := []searchTest{}
 	for _, test := range tests {
-		if utils.StringInSlice(EngineAll, test.Tags) {
+		if pUtils.Contains(test.Tags, EngineAll) {
 			filteredTests = append(filteredTests, test)
 			continue
 		}
 		for _, tag := range tags {
-			if utils.StringInSlice(tag, test.Tags) {
+			if pUtils.Contains(test.Tags, tag) {
 				filteredTests = append(filteredTests, test)
 				break
 			}