backend webhook send email to user notifying them of their booking

[bcho892]

Made use of https://medium.com/@y.mehnati_49486/how-to-send-an-email-from-your-gmail-account-with-nodemailer-837bf09a7628 to send directly from a gmail account using an app password.

also updated workflows, will update wiki soon with the new envs

Also closes #461

NODE_MAILER_EMAIL and NODE_MAILER_PASSWORD

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 9da97e8):

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