Convert Jira issue references to GitHub issues

[MarkEWaite]

Convert Jira issue references to GitHub issue references

Fixes #2585

• Update process descriptions to replace Jira with GitHub issues
• Update URLs in plugin help text
• Update links in job-dsl-core
• Update links in several documentation files
• Use issue redirector for issue links

Did not change all wiki references.

Testing done

Checked each modified URL resolves to a useful page.

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 demonstrate the feature works or the issue is fixed