Refactor handlebar effects to allow public retrieve

[minottic]

Description

Refactor handlebar effects to allow public retrieve

Motivation

A case where a public job is submitted but still has to apply some retrieve features was needed. One can enable it, by setting the value config.smtpMessage.publicRetrieve to true.

Changes:

• server/boot/handleJobSideEffects.js refactor

Tests included/Docs Updated?

• [ ] Included for each change/fix?
• [x] Passing? (Merge will not be approved unless this is checked)
• [ ] Docs updated?
• [ ] New packages used/requires npm install?
• [x] Toggle added for new features?

[minottic]

@marcoleorato I did some refactoring of the handlebarsEffect.js, and I think you use it as well. Could you please review this PR, to make sure it does not inadvertently break features?