How can I update a jira issue from within a Jenkinsfile (jenkins-worflow/pipeline)? Is there a way I could use the Jira Issue Updater plugin as a step in the Jenkinsfile?
Yes, seems like this page answers your question:
https://wiki.jenkins-ci.org/display/JENKINS/Jira+Issue+Updater+Plugin
After you install the plugin, add a build step, or pre/post build step to call this plugin
There you can give it the REST URL to your Jira server, the creds and the JQL to find the issues