fix: return proper error if sms rate limit is exceeded (supabase#1647)

## What kind of change does this PR introduce?
* Fixes supabase#1629 
* Previously, rate limit errors were being returned as an internal
server error, which is incorrect. This PR checks for the underlying
error type returned and ensures that rate limit errors are surfaced
appropriately.

## What is the current behavior?

Please link any relevant issues here.

## What is the new behavior?

Feel free to include screenshots if it includes visual changes.

## Additional context

Add any other context or screenshots.

internal/api/user.go

@@ -236,6 +236,9 @@ func (a *API) UserUpdate(w http.ResponseWriter, r *http.Request) error {
 					return internalServerError("Error finding SMS provider").WithInternalError(terr)
 				}
 				if _, terr := a.sendPhoneConfirmation(r, tx, user, params.Phone, phoneChangeVerification, smsProvider, params.Channel); terr != nil {
+					if errors.Is(terr, MaxFrequencyLimitError) {
+						return tooManyRequestsError(ErrorCodeOverSMSSendRateLimit, generateFrequencyLimitErrorMessage(user.PhoneChangeSentAt, config.Sms.MaxFrequency))
+					}
 					return internalServerError("Error sending phone change otp").WithInternalError(terr)
 				}
 			}