Upgrade API usage of javamail

In LTS2019 and LTS2021, Nuxeo uses lib\mail-1.4.x.jar to support sending mail (SMTP)

Nuxeo also uses API such as:

config.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");

which dates from JavaMail 1.3

Previously Java Mail API (up to JavaMail 1.3) didn’t have built-in support for SSL connection, so it was necessary to set socketFactory properties:

Properties props = new Properties();
props.put("mail.smtp.socketFactory.class","javax.net.ssl.SSLSocketFactory");

From the later version of Java Mail API (greater than 1.3).

The easiest way to enable SSL support in current versions of JavaMail is to set the property "mail.smtp.ssl.enable" to "true".

props.put("mail.smtp.ssl.enable", "true");

Once this is enabled, you are ready to use SSL for authentication.

This might require to change some administratively declared Nuxeo properties, e.g.
mail.transport.protocol from smtp to smtps...

Implementing this change would enable to upgrade to mail-1.6.x.jar and leverage https://javaee.github.io/javamail/docs/SSLNOTES.txt ...