MM-33913: Fix read-after-write issues with team member (#17173)

During LDAP sync, we would call AddTeamMember which had a read-after-write issue
where we would create a team member but then immediately after that
query the team member.

The same pattern was found in:
AddTeamMember
AddTeamMembers
AddTeamMemberByToken

To fix this, we just return the inserted team member from AddUserToTeam and use that
instead of query GetTeamMember again.

```release-note
NONE
```

https://mattermost.atlassian.net/browse/MM-33913

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

api4/apitestlib.go

@@ -781,7 +781,7 @@ func (th *TestHelper) UpdateActiveUser(user *model.User, active bool) {
 func (th *TestHelper) LinkUserToTeam(user *model.User, team *model.Team) {
 	utils.DisableDebugLogForTest()
 
-	err := th.App.JoinUserToTeam(team, user, "")
+	_, err := th.App.JoinUserToTeam(team, user, "")
 	if err != nil {
 		panic(err)
 	}