[actions] improve email action doc

resolves elastic#88333

Fixed:

- add note that `secure: false` will use TLS, but after an initial connection
  with TCP; we have been getting questions from customers who believed that
  `secure: false` implied TLS was not used at all.

- added a link to the nodemailer "well-known services" module, to allow
  customers to see examples of other email service configurations

- updated the Outlook config example to use the current nodemailer values

- couple of other small tweaks

docs/user/alerting/action-types/email.asciidoc

@@ -14,7 +14,7 @@ Name::      The name of the connector. The name is used to identify a  connector
 Sender::    The from address for all emails sent with this connector, specified in `user@host-name` format.
 Host::      Host name of the service provider. If you are using the <<action-settings, `xpack.actions.allowedHosts`>> setting, make sure this hostname is added to the allowed hosts.
 Port::      The port to connect to on the service provider.
-Secure::    If true the connection will use TLS when connecting to the service provider. See https://nodemailer.com/smtp/#tls-options[nodemailer TLS documentation] for more information.
+Secure::    If true the connection will use TLS when connecting to the service provider. See https://nodemailer.com/smtp/#tls-options[nodemailer TLS documentation] for more information.  If not true, the connection will initially connect over TCP, then attempt to switch to TLS via the SMTP STARTTLS command.
 Username::  username for 'login' type authentication.
 Password::  password for 'login' type authentication.
 
@@ -92,6 +92,8 @@ systems, refer to:
 * <<exchange>>
 * <<amazon-ses>>
 
+For other email servers, you can check the list of well-known services that Nodemailer supports in the JSON file https://github.com/nodemailer/nodemailer/blob/master/lib/well-known/services.json[well-known/services.json].  The properties of the objects in those files - `host`, `port`, and `secure` - correspond to the same email action configuration properties.  A missing `secure` property in the "well-known/services.json" file is considered `false`.
+
 [float]
 [[gmail]]
 ===== Sending email from Gmail
@@ -109,7 +111,6 @@ https://mail.google.com[Gmail] SMTP service:
     user: <username>
     password: <password>
 --------------------------------------------------
-// CONSOLE
 
 If you get an authentication error that indicates that you need to continue the
 sign-in process from a web browser when the action attempts to send email, you need
@@ -131,9 +132,9 @@ https://www.outlook.com/[Outlook.com] SMTP service:
 [source,text]
 --------------------------------------------------
 config:
-    host: smtp-mail.outlook.com
-    port: 465
-    secure: true
+    host: smtp.office365.com
+    port: 587
+    secure: false
 secrets:
     user: <email.address>
     password: <password>
@@ -163,7 +164,7 @@ secrets:
     user: <username>
     password: <password>
 --------------------------------------------------
-<1> `smtp.host` varies depending on the region
+<1> `config.host` varies depending on the region
 
 NOTE:   You must use your Amazon SES SMTP credentials to send email through
         Amazon SES. For more information, see