Update email templates for user group

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Right now the emails are very confusing, need to update to make more sense for the following:

Verification message
A verification message can be sent automatically when a user signs up, or alternatively, a verification message may be sent by using a pre-sign up Lambda trigger or by calling the AdminConfirmSignUp API.

Invitation message
Invitation messages are sent when creating a user via the console or by calling the AdminCreateUser API.

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also checkout Resend to send via a vanity domain

and DeMarc compliance to make sure emails go through.