Replace MailHog with MailPit

[spwoodcock]

• https://github.com/axllent/mailpit
• A better maintained and faster alternative to mailhog - it serves the same purpose
• I heard about it becasue it's used in the ODK Central dev setup.
• I also now use it in FieldTM dev compose config and it works well:

  mail:
    image: "axllent/mailpit:v1.29.2"
    networks:
      - ftm-net
    restart: "unless-stopped"

[linear]

TECH-1017

[emi420]

This is very low priority because it's barely used for development, @spwoodcock could you explain what are the benefits of investing time in changing this? thanks!