Kibana version: 7.11.0 - worked on releases up to this though

Describe the bug:

Email servers that don't support TLS cannot be used with Kibana 7.11.0, but worked in previous versions. The best example is using the maildev npm package. If you run via npx maildev (no need to install anything), it will launch a mail server and a web client to read the emails that get sent.

$ npx maildev
npx: installed 118 in 6.567s
MailDev webapp running at http://0.0.0.0:1080
MailDev SMTP Server running at 0.0.0.0:1025

When sending an email through this server in 7.11.0, you'll see the following error:

error sending email: self signed certificate

We are seeing a similar issue with a cloud email proxy, not clear if it's the same, but sounds like it is, as it also does not support TLS AFAIK.

Steps to reproduce:

I have a pre-configured action for maildev in my kibana.dev.yml file, but you can also create the same one manually:

xpack.actions.preconfigured:
  maildev-no-auth:
    name: 'email: maildev no auth'
    actionTypeId: '.email'
    config:
      from: 'from@example.com'
      host: 'localhost'
      port: '1025'

From the Kibana UI, find this connector, and then go to the test tab. Fill in the To / Subject / Message fields, and click the Run button. You should see the error message in the Results section.