[Photos][Server] Cannot Connect Clear SMTP Postfix From Server

[dinobagio]

As discussed here:
https://discord.com/channels/948937918347608085/1478332406334488576

There is an issue when trying to connect a local Postfix relay in clear (port 25, no TLS)
Because here:
https://github.com/ente-io/ente/blame/b877d6530f66ee083a2ae3359c25f5cd6d67ff96/server/pkg/utils/email/email.go#L229

This function will auto upgrade with STARTTLS is proposed on ehlo by smtp server.

Online doc says:
Workaround: Use smtp.Client manually
If you need to avoid TLS entirely (e.g., for testing or internal servers), use smtp.Client and don’t call StartTLS.

As a consequence, we cannot enroll new users, because then it tries to STARTTLS and then verify a certificate it cannot verify since default postfix cert is non public.