docs[confluent]: add docs for new confluent plugin

app/_hub/kong-inc/confluent/_changelog.md

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+## Changelog
+
+**{{site.base_gateway}} 3.8.x**
+
+Added plugin

app/_hub/kong-inc/confluent/_metadata/_index.yml

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+name: Confluent
+search_aliases:
+  - confluent
+dbless_compatible: 'yes'
+free: false
+enterprise: true
+paid: true
+konnect: true
+network_config_opts: All
+notes: --
+categories:
+  - transformations
+publisher: Kong Inc.
+desc: Transform requests into Kafka messages in a Confluent topic.

app/_hub/kong-inc/confluent/overview/_index.md

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+---
+nav_title: Overview
+---
+
+!! Put an intro to Confluent here. !!
+
+<!-- I modified this a bit to point to Apacha  Kafka installations -->
+Kong also provides a Kafka Log as well as Kafka Upstream plugin for publishing logs and messages to a Apache Kafka topic.
+
+* See [Kafka Log](/hub/kong-inc/kafka-log/)
+* See [Kafka Upstream](/hub/kong-inc/kafka-upstream/)
+
+## Enable on a service-less route
+
+```bash
+curl -X POST http://localhost:8001/routes/my-route/plugins \
+    --data "name=confluent" \
+    --data "config.bootstrap_servers[1].host=localhost" \
+    --data "config.bootstrap_servers[1].port=9092" \
+    --data "config.cluster_api_key=my-api-key" \
+    --data "config.cluster_api_secret=my-api-secret" \
+    --data "config.topic=my-confluent-topic" \
+```
+
+## Known issues and limitations
+
+Known limitations:
+
+1. Message compression is not supported.
+2. The message format is not customizable.
+
+## Quickstart
+
+The following steps assume that {{site.base_gateway}} is installed and the Confluent plugin is enabled.
+
+<!-- Add instructions here on how to Setup a Confluent Cluster or point to upstream documentation -->
+
+Make sample requests:
+
+    ``` bash
+    curl -X POST http://localhost:8000 --header 'Host: confluent.dev' foo=bar
+    ```
+
+    You should receive a `200 { message: "message sent" }` response, and should see the request bodies appear on
+    the Confluent (what's the equivalent in Conlfuent Cloud here?) consumer console you started in the previous step.

app/_hub/kong-inc/confluent/versions.yml

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+strategy: gateway
+releases:
+  minimum_version: '2.1.x'
+
+overrides:
+  2.8.x: 0.4.0
+  2.7.x: 0.3.0
+  2.6.x: 0.2.0
+  2.5.x: 0.0.2
+  2.4.x: 0.0.2
+  2.3.x: 0.0.2
+  2.2.x: 0.0.2
+  2.1.x: 0.0.2