Add support for SMTP (sending emails)

[root-kidik]

VMime mailio libquickmail NwSMTP pure curl

[Anton3]

userver uses libcurl for HTTP client. libcurl also supports SMTP, but this support is not exposed in userver (one, two, three).

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There is no workaround to this missing support. Basically the alternatives are to either contribute this, or use another service based on another server framework for sending emails. A random lib cannot be used with userver, because it blocks thread, and a proper integration might be more difficult than exposing the necessary libcurl features.