root: global email settings (#448)

* root: make global email settings configurable

* stages/email: add use_global_settings

* stages/email: add test_email command to test email sending

* stages/email: update email template

* stages/email: simplify email template path

* stages/email: add support for user-supplied email templates

* stages/email: add tests for sending and templates

* stages/email: only add custom template if permissions are correct

* docs: add custom email template docs

* root: add /templates volume in docker-compose by default

* stages/email: fix form not allowing custom templates

* stages/email: use relative path for custom templates

* stages/email: check if all templates exist on startup, reset

* docs: add global email docs for docker-compose

* helm: add email config to helm chart

* helm: load all secrets with env prefix

* helm: move s3 and smtp secret to secret

* stages/email: fix test for relative name

* stages/email: add argument to send email from existing stage

* stages/email: set uid using slug of message id

* stages/email: ensure template validation ignores migration runs

* docs: add email troubleshooting docs

* stages/email: fix long task_name breaking task list

website/docs/troubleshooting/emails.md

@@ -0,0 +1,23 @@
+---
+title: Troubleshooting Email sending
+---
+
+To test if an email stage, or the global email settings are configured correctly, you can run the following command:
+
+````
+./manage.py test_email <to address> [-s <stage name>]
+```
+
+If you omit the `-s` parameter, the email will be sent using the global settings. Otherwise, the settings of the specified stage will be used.
+
+To run this command with docker-compose, use
+
+```
+docker-compose exec -it worker ./manage.py test_email [...]
+```
+
+To run this command with Kubernetes, use
+
+```
+kubectl exec -it authentik-worker-xxxxx -- ./manage.py test_email [...]
+```