This PR add Inbound Email integration.
It designed to support some variety of ESPs, but in prod we will use
Mailgun, so locally I tested it only with mailgun ESP.
**Important:**
To make it work on different clusters I'm planning to provide different
email domains for different regions, like ....@us.oncall.grafana.net,
...@eu.oncall.grafana.net
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Co-authored-by: Innokentii Konstantinov <innokenty.konstantinov@grafana.com>
Also changes the default integration used when creating an alert group
for a direct page to a custom manual integration to avoid
conflicts/unexpected behaviors with existing manual alerts.
* remove email verification related code
* remove email verification related code
* remove sendgrid callback
* remove sendgrid related code
* remove sendgrid related code
* rename sendgrid app to email
* remove email from built-in channels
* remove email from built-in channels
* remove email from built-in channels
* add email backend: https://github.com/grafana/oncall/pull/50
* add email templater
* add email templater
* convert md to html
* add email settings to live settings
* use task to send email, handle some exceptions to create logs
* remove ERROR_NOTIFICATION_MAIL_DELIVERY_FAILED usage
* add email limit logic
* fix tests
* add docs
* remove old email templates
* remove old email templates
* add template_fields to messaging backend
* add messaging backends templates to public api
* add comment for deprecated fields
* fix test
* fix tests
* disable email by default
* don't retry on SMTPException and TimeoutError
* add tests
* bring email back to public api docs
* return ERROR_NOTIFICATION_MAIL_LIMIT_EXCEEDED
* make template_fields tuple
* build_subject_and_title -> build_subject_and_message
* add one more comment about template deprecation
* use 8 as backend id
* add comment about gaierror and BadHeaderError
* add comment on importing in notify_user_async
* edit oss docs
* use web title template to render alert group verbose name
* remove group_verbose_name from tests
* clean up group_verbose_name
* remove verbose_name from API & plugin
* verbose_name migration
* update verbose name on web title template change
* use long queue for updating verbose name
* use first alert for updating verbose name
* improve batch_ids
* fix update_verbose_name
* post-review fixes
* post-review fixes
* use web title template to render alert group verbose name
* remove group_verbose_name from tests
* clean up group_verbose_name
* remove verbose_name from API & plugin
* verbose_name migration
* update verbose name on web title template change
* use long queue for updating verbose name
* use first alert for updating verbose name
* improve batch_ids
* Fix creation of manual incident via submenu
* Remove legacy finish_configuration_attachments
* Add manual incidents for all teams
* Fix manual incident creation from slash command
* Fix slack title template
* Get rid of migration
