Extracting email functions into a service (#14802)

* Extracting email functions into a service

* Fixing two shadowing errors

* Address PR review comments

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

api4/user_test.go

@@ -3068,7 +3068,7 @@ func TestVerifyUserEmail(t *testing.T) {
 
 	ruser, _ := th.Client.CreateUser(&user)
 
-	token, err := th.App.CreateVerifyEmailToken(ruser.Id, email)
+	token, err := th.App.Srv().EmailService.CreateVerifyEmailToken(ruser.Id, email)
 	require.Nil(t, err, "Unable to create email verify token")
 
 	_, resp := th.Client.VerifyUserEmail(token.Token)