Migrate from Bamboo to Swoosh for email sending

[mayel]

related to

• https://github.com/bonfire-networks/bonfire-app/issues/559
• https://github.com/bonfire-networks/bonfire-app/issues/688
• https://github.com/bonfire-networks/bonfire-app/issues/729

[mayel]

Added support for swoosh in bonfire_mailer (as a configurable adapter so bamboo can still be used) but have yet to

• [x] update the config (generate from env vars)
• [ ] integrate https://github.com/swoosh/phoenix_swoosh for templated messages?