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/public/model/command_autocomplete.go

@@ -11,6 +11,8 @@ import (
 	"strings"
 
 	"github.com/pkg/errors"
+
+	"github.com/mattermost/mattermost/server/public/utils"
 )
 
 // AutocompleteArgType describes autocomplete argument type
@@ -234,7 +236,7 @@ func (ad *AutocompleteData) IsValid() error {
 		return errors.New("Command should be lowercase")
 	}
 	roles := []string{SystemAdminRoleId, SystemUserRoleId, ""}
-	if stringNotInSlice(ad.RoleID, roles) {
+	if !utils.Contains(roles, ad.RoleID) {
 		return errors.New("Wrong role in the autocomplete data")
 	}
 	if len(ad.Arguments) > 0 && len(ad.SubCommands) > 0 {
@@ -399,12 +401,3 @@ func (a *AutocompleteArg) UnmarshalJSON(b []byte) error {
 	}
 	return nil
 }
-
-func stringNotInSlice(a string, slice []string) bool {
-	for _, b := range slice {
-		if b == a {
-			return false
-		}
-	}
-	return true
-}