DEV: replace mailcatcher references with mailhog (PR #14500)

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I think we still need to install bundler and rake here?

Good catch! I’ve made the required change.

Similar to my comment in discourse_docker, I don’t think this makes mailhog available on the PATH. We might want to move the binary to somewhere on the PATH (and maybe rename it to mailhog? Uppercase characters in the binary name seems a little weird)