Add codeowner

[jonesbusy]

After seeing on one of my plugin

I've used the tool https://github.com/jenkinsci/plugin-modernizer-tool

For the moment is rather a manual process because we don't have any git/jgit or github integration but the concept seems to work

# Build it because we don't have releases yet
mvn clean install 

# Clone the forked repo
git clone git@github.com:jonesbusy/extension-filter-plugin.git test-plugins/extension-filter-plugin

# The the recipe
java -jar plugin-modernizer-cli/target/jenkins-plugin-modernizer-999999-SNAPSHOT.jar --plugins extension-filter-plugin --recipes AddCodeOwner

# Commit and push
git -C test-plugins/extension-filter-plugin checkout -b feature/code-owner
git -C test-plugins/extension-filter-plugin add .
git -C test-plugins/extension-filter-plugin commit -m "Add codeowner"
git -C test-plugins/extension-filter-plugin push origin feature/code-owner 

Testing done

Submitter checklist

• [ ] Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• [ ] Ensure that the pull request title represents the desired changelog entry
• [ ] Please describe what you did
• [ ] Link to relevant issues in GitHub or Jira
• [ ] Link to relevant pull requests, esp. upstream and downstream changes
• [ ] Ensure you have provided tests - that demonstrates feature works or fixes the issue