💡 [Feature] SMTP configuration for services that need it

[fmigneault]

Description

Following features required a SMTP configuration to be defined in order to add more functionalities:

• Weaver
  • Email notification following job completion
    see https://github.com/bird-house/birdhouse-deploy/pull/114/files/e5053d28cace612f5a97fed28d4a59b3b1de8d39#r737808155
• Magpie:
  • Approval email from Group join with Terms and Conditions (Feature add tc Ouranosinc/Magpie#467)
  • Confirmation/approval email from User self-registering (User self-registration Ouranosinc/Magpie#435)

Variables should be made available for easy overrides to be pushed within configuration files of each relevant services.
Empty defaults should be used to preserve features inactive (current behaviour).

Concerned Organizations

Any that what's to make sure of those features.