Split EMAIL_PROVIDER_PARAMS into components

[AntonOfTheWoods]

As many configuration management systems use JSON (including via YAML) for defining config, having a JSON string that goes into an env var causes significant extra friction. There are only 5 values, could these be split out into normal env vars, at least as an option (so add SMTP_HOST, SMTP_PORT, etc. and use EMAIL_PROVIDER_PARAMS if present, then falling back to SMTP_* if not)?