Adds a ratelimit for AmazonSNS.
AlertChannelDefining mixin is now injecting alert_receive_channel only
in request, not in kwargs to not to break AmazonSNS.
# What this PR does
Fix inbound email endpoint bug when attaching files to email leads to
HTTP 500.
## Checklist
- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] `CHANGELOG.md` updated (or `pr:no changelog` PR label added if not
required)
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>
