[MM-49989] Pass a context.Context to Client4 methods (#22922)

* Migrate all method in model/client4.go to accept a context.Context

* Fix th.*Client

* Fix remaining issues

* Empty commit to triger CI

* Fix test

* Add cancellation test

* Test that returned error is context.Canceled

* Fix bad merge

* Update mmctl code

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/slashcommands/command_loadtest.go

@@ -4,6 +4,7 @@
 package slashcommands
 
 import (
+	"context"
 	"encoding/json"
 	"io"
 	"net/http"
@@ -248,7 +249,7 @@ func (*LoadTestProvider) SetupCommand(a *app.App, c request.CTX, args *model.Com
 		if err := CreateBasicUser(a, client); err != nil {
 			return &model.CommandResponse{Text: "Failed to create testing environment", ResponseType: model.CommandResponseTypeEphemeral}, err
 		}
-		_, _, err := client.Login(BTestUserEmail, BTestUserPassword)
+		_, _, err := client.Login(context.Background(), BTestUserEmail, BTestUserPassword)
 		if err != nil {
 			return &model.CommandResponse{Text: "Failed to create testing environment", ResponseType: model.CommandResponseTypeEphemeral}, err
 		}
@@ -604,7 +605,7 @@ func (*LoadTestProvider) PostCommand(a *app.App, c request.CTX, args *model.Comm
 	}
 
 	client := model.NewAPIv4Client(args.SiteURL)
-	_, _, nErr := client.LoginById(user.Id, passwd)
+	_, _, nErr := client.LoginById(context.Background(), user.Id, passwd)
 	if nErr != nil {
 		return &model.CommandResponse{Text: "Failed to login a user", ResponseType: model.CommandResponseTypeEphemeral}, nErr
 	}
@@ -613,7 +614,7 @@ func (*LoadTestProvider) PostCommand(a *app.App, c request.CTX, args *model.Comm
 		ChannelId: channel.Id,
 		Message:   textMessage,
 	}
-	_, _, nErr = client.CreatePost(post)
+	_, _, nErr = client.CreatePost(context.Background(), post)
 	if nErr != nil {
 		return &model.CommandResponse{Text: "Failed to create a post", ResponseType: model.CommandResponseTypeEphemeral}, nErr
 	}