Make the SMTP client used in javascript templates able to send email

[Marcuccio]

Closes #4444

Proposed changes

With the proposed change, the SMTPmodule used in the Javascript Protocol will have the SMTPClient struct able to test open relay with the new function IsOpenRelay()

I tested the new feature with a postfix server in my local PC and with destination a random temporary mail service found on internet.

I tested the code with the below template:

id: smtp-open-relay

info:
  name: SMTP open relay - Exploit
  author: abut0n
  severity: High
  description: |
    Mail relaying allows any spammer or phisher to abuse a mail server and send unsolicited mails, thus flooding network bandwidth or enabling [spear-]phishing attacks.
  reference:
    - https://nmap.org/nsedoc/scripts/smtp-open-relay.html
  tags: network,js,smtp,mail

javascript:
  - code: |
      var m = require("nuclei/smtp");
      var c = m.SMTPClient();
      msg = m.NewSMTPMessage();
      msg.From(template.From);
      msg.To(template.To);
      msg.Subject(template.Subj);
      msg.Body(template.Msg);
      var response = c.IsOpenRelay(Host, Port, msg);
      to_json(response);
    
    args:
      Host: "{{Host}}"
      Port: "25"
      Subj: "Open relay at: {{Host}}"
      Msg: "Contact your security team if you do not expect this message"

    matchers:
      - type: word
        words:
          - true

And obtained the expected behavior debugging with:

go run cmd/nuclei/main.go -code -t smtp-open-relay.yaml -debug -u 127.0.0.1 -var From="[email protected]" -var To="<your@destination>" 

Checklist

• [x ] Pull request is created against the dev branch
• All checks passed (lint, unit/integration/regression tests etc.) with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[tarunKoyalwar]

lgtm !

• misc changes like network host deny policy etc
• updated js docs + bindings
• added SMTPMessage builder struct to build message with options

public smtp server = https://www.wpoven.com/tools/free-smtp-server-for-testing