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>

app/user.go

@@ -96,7 +96,7 @@ func (a *App) CreateUserWithToken(user *model.User, token *model.Token) (*model.
 		return nil, err
 	}
 
-	if err := a.JoinUserToTeam(team, ruser, ""); err != nil {
+	if _, err := a.JoinUserToTeam(team, ruser, ""); err != nil {
 		return nil, err
 	}
 
@@ -149,7 +149,7 @@ func (a *App) CreateUserWithInviteId(user *model.User, inviteId, redirect string
 		return nil, err
 	}
 
-	if err := a.JoinUserToTeam(team, ruser, ""); err != nil {
+	if _, err := a.JoinUserToTeam(team, ruser, ""); err != nil {
 		return nil, err
 	}