MINOR: Update introduction page in Kafka documentation
Although APIs section in Kafka documentation lists 5 core APIs (https://kafka.apache.org/documentation/#api), introduction page in Kafka documentation lists 4 of them. I've added the missing list element to fix this incoherence.
Reviewers: Manikumar Reddy
<li>The Kafka cluster stores streams of <i>records</i> in categories called <i>topics</i>.
<li>Each record consists of a key, a value, and a timestamp.
</ul>
- <p>Kafka has four core APIs:</p>
+ <p>Kafka has five core APIs:</p>
<div style="overflow: hidden;">
<ul style="float: left; width: 40%;">
<li>The <a href="/documentation.html#producerapi">Producer API</a> allows an application to publish a stream of records to one or more Kafka topics.
<li>The <a href="/documentation.html#consumerapi">Consumer API</a> allows an application to subscribe to one or more topics and process the stream of records produced to them.
<li>The <a href="/documentation/streams">Streams API</a> allows an application to act as a <i>stream processor</i>, consuming an input stream from one or more topics and producing an output stream to one or more output topics, effectively transforming the input streams to output streams.
<li>The <a href="/documentation.html#connect">Connector API</a> allows building and running reusable producers or consumers that connect Kafka topics to existing applications or data systems. For example, a connector to a relational database might capture every change to a table.
+ <li>The <a href="/documentation.html#adminapi">Admin API</a> allows managing and inspecting topics, brokers and other Kafka objects.
</ul>
<img src="/{{version}}/images/kafka-apis.png" style="float: right; width: 50%;">
</div>
