feat: add MailHog to docker-compose.yaml

[kenjis]

See https://github.com/mailhog/MailHog

[MGatner]

MailHog looks cool but hasn't had a release in 2 years. Is this what we want to endorse? Have you used it recently and verified it still works well?

[kenjis]

I checked it worked today.

Are there any other mail servers that are easy to build?

[MGatner]

I've never used such a service! I always mock the email class and capture output instead (see Tatter\Outbox for example).

I'm interested in trying this though. Let's go with this one since you have experience with it.

[kenjis]

Yes, this is just some lines in docker-compose.yaml.
If we find something better, it is very easy to change.

MailHog is also very easy. set .env and run docker-compose.
That's it. You can see sent mails in http://localhost:8025/