Add download option to 'Console output', move 'View as plain text' and 'Copy' buttons to app bar

[janfaracik]

Companion to https://github.com/jenkinsci/jenkins/pull/9169. Adds a download option to 'Console output', moves 'View as plain text' and 'Copy' buttons to the app bar. Requires 9169 as a base to show the actions in the app bar, otherwise doesn't show on lower versions of Jenkins - nothing breaks.

Would be good to have the console page be extensible and have this plugin replace just the parts it needs - but out of scope for this PR.

Testing done

• Copy button works as before
• View as plain text works as before
• Download button downloads the full log

Submitter checklist

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