Email notification service must support encrypted parameters

Working scenario (authenticated SMTP traffic but unencrypted parameter mail.transport.password)

1. install nuxeo
2. add the following parameters to nuxeo.conf:

   mail.transport.port=2525
   mail.transport.user=toto
   mail.transport.password=password
   mail.transport.auth=true
   

3. uncomment the following line in nuxeo.conf to allow debugging

   JAVA_OPTS=$JAVA_OPTS -Xdebug -Xrunjdwp:transport=dt_socket,address=8787,server=y,suspend=n
   

4. start the server
5. start a python debug server on port 2525:

   sudo python -m smtpd -n -c DebuggingServer localhost:2525

6. login as Administrator
7. create a workspace
8. create a document in the workspace
9. go the Administration tab
10. start a debugging session in your preferred IDE
11. set a breakpoint in EmailHelper on this line:
    https://github.com/nuxeo/nuxeo/blob/release-9.10-HF05/nuxeo-features/nuxeo-platform-notification/nuxeo-platform-notification-core/src/main/java/org/nuxeo/ecm/platform/ec/notification/email/EmailHelper.java#L111
12. in the Notifications sub-tab register the Administrator user on New comment event.
13. the breakpoint should be enabled right after
14. in the variables, check the content of session.authenticator.properties and observe:

    mail.smtp.password=password

15. stop the debugging session
16. stop the server

Non-working scenario (authenticated SMTP traffic but encrypted parameter mail.transport.password)

1. encrypt the password with the following commands:

   nuxeoctl config server.crypt.secretkey --set -q
   nuxeoctl config mail.transport.password --encrypt --set -q
   

2. when prompted set the password as password
3. to double-check the encrypted password is decryptable use the following:

   nuxeoctl decrypt 'encryption string'
   

4. start the server
5. login as Administrator
6. create a document in the workspace
7. go the Administration tab
8. start a debugging session in your preferred IDE
9. set a breakpoint in EmailHelper on this line:
   https://github.com/nuxeo/nuxeo/blob/release-9.10-HF05/nuxeo-features/nuxeo-platform-notification/nuxeo-platform-notification-core/src/main/java/org/nuxeo/ecm/platform/ec/notification/email/EmailHelper.java#L111
10. in the Notifications sub-tab register the Administrator user on New comment event.
11. the breakpoint should be enabled right after
12. in the variables, check the content of session.authenticator.properties and observe:

    mail.smtp.password=${mail.transport.password}

Impact: this prevents using authentication to a mail server. It works fine when not encrypting the parameter. For instance, this means notifications cannot be sent in this case.

Expected behavior: the parameter should be correctly decrypted.