Recover Kafka notes and make reference to deployment notes (#13880)

Recover changes from #13834 and point to more detailed instructions in
the shared Kafka README file.

Author: armenzg

develop-docs/backend/application-domains/kafka.mdx

@@ -3,4 +3,34 @@ title: Kafka consumers
 sidebar_order: 60
 ---
 
-Visit https://github.com/getsentry/ops/tree/master/shared_config/kafka for a full, in-depth step-by-step guide.
+## Create a new Kafka topic
+
+1. Add the topic to the `KAFKA_TOPIC_TO_CLUSTER` in [src/sentry/conf/server.py](https://github.com/getsentry/sentry/blob/master/src/sentry/conf/server.py):
+  * e.g. `subscription-results-eap-items`
+2. Add the topic to `Topic` in [src/sentry/conf/types/kafka_definition.py](https://github.com/getsentry/sentry/blob/master/src/sentry/conf/types/kafka_definition.py)
+
+## Define or re-use a processing strategy
+
+In most cases a [Streaming Factory](https://getsentry.github.io/arroyo/getstarted.html#create-a-streaming-consumer) is what you want to when defining a consumer (see next section). You can find examples of it in [Sentry's code base](https://github.com/search?q=repo%3Agetsentry%2Fsentry+%28ProcessingStrategyFactory&type=code).
+
+## Define a new Kafka consumer
+
+1. Add a new entry in the `KAFKA_CONSUMERS` key in
+   [src/sentry/consumers/__init__.py](https://github.com/getsentry/sentry/blob/master/src/sentry/consumers/__init__.py):
+```python
+KAFKA_CONSUMERS = {
+    "<your_topic_str_here>": {
+        "topic": Topic.YOUR_TOPIC,
+        "strategy_factory": "sentry_package_defining_your_strategy_factory_class",
+    }
+}
+```
+2. You may need optional properties (e.g. `click_options`, you will need to research them by looking at [ConsumerDefinition](https://github.com/getsentry/sentry/blob/master/src/sentry/conf/types/kafka_definition.py)'s code.
+
+3. Make sure you can run it: `sentry run consumer <your_topic>`
+4. You may need to add some devserver options [here](https://github.com/getsentry/sentry/blob/master/src/sentry/runner/commands/devserver.py).
+4. Add tests for your consumer
+
+## Deployment
+
+Visit the Ops repo and search for `shared_config/kafka/README.md` for a full, in-depth step-by-step guide.

docs/organization/integrations/issue-tracking/incidentio/img/incidentio-alert-rule.png

@@ -13,7 +13,6 @@ This integration is maintained and supported by the company that created it. For
 <Alert>
 
 Sentry owner, manager, or admin permissions are required to install this integration.
-
 incident.io **won't** work with self-hosted Sentry.
 
 </Alert>
@@ -40,7 +39,7 @@ The Sentry issue is now attached to the incident:
 
 ![Incident with Sentry issue attached](./img/incidentio-attach-post.png)
 
-### In sentry.io
+### In Sentry
 
 To attach a Sentry issue to an incident in [sentry.io](https://sentry.io), navigate to a specific Sentry issue and find the "Linked Issues" section on the right panel. Click "Link incident.io issue" and select your active incident from the dropdown:
 
@@ -51,3 +50,17 @@ To attach a Sentry issue to an incident in [sentry.io](https://sentry.io), navig
 The incident's Slack channel will be updated with attached Sentry issue comments, edited comments, and when the Sentry issue is resolved:
 
 ![Synced comments from Sentry on an incident in Slack](./img/incidentio-issue-sync.png)
+
+
+## Alerting
+
+Once installed, you can also set Sentry to be an alert source for incidents.
+
+![incident.io alert setup](./img/incidentio-alert-setup.png)
+
+Afterward, within Sentry you can connect it to that newly created source in an alert rule.
+
+![incident.io alert rule](./img/incidentio-alert-rule.png)
+
+
+When the alert fires, it'll create an incident on incident.io, with all the downstream affects you set up on that side.