exim4 is phaseout

[lcgogo]

According to https://develop.sentry.dev/self-hosted/email/ sentry self hosted is using exim4

But exim4 is phaseout
https://hub.docker.com/r/tianon/exim4

NOTE
I've personally stopped using this image! These days I just use msmtp⁠ instead, which gives my application direct feedback on the success/failure instead of filling up a "frozen" queue in exim4 that I then also have to manage. At some point, I'll probably stop maintaining this image entirely.

[aldy505]

Hopefully not gonna cause any issues in the future. But I'd prefer we move to this though https://hub.docker.com/r/ixdotai/smtp, since it also support arm64.