for most config settings, I tend to prefer english_words_with_underscores.

Based on the zulip docs, they seem to call this "bot email address"  and the key is called "bot api key"

From https://zulip.com/api/endpoints/
>     -u BOT_EMAIL_ADDRESS:BOT_API_KEY

Thoughts on aligning the terminology with what zulip uses in their docs?

Alternately, since this is just used for http authentication, and we try to keep all logstash plugins using the same terms for auth, name this `user` and `password` ?