fix: update MaxFrequency error message to reflect number of seconds

[J0]

What kind of change does this PR introduce?

Currently we use a constant value on number of seconds left before a developer can send a follow up email confirmation. This can prove confusing if developer has a custom setting for MaxFrequency on Sms or SMTP

Considered pushing the check into validateFrequencyLimit in sendConfirmationMail or similar. Unfortunately, that would obscure the existing error message and return an internalServerError instead which might be harder to interpret for a dev