Check a plugin exists within a Jenkins Pipeline (Groovy)
<p>I want to use the Slack Notification Plugin in my pipelines, which is very easy:</p>

<pre><code>slackSend color: 'danger', message: 'Everything broke'
</code></pre>

<p>However, I don't want the build to break if slackSend doesn't exist. Is there a way to check that first?</p>