Add support to backup and restore automatically

[LinuxSuRen]

This feature provides a solution to allow users to upgrade their Jenkins Configuration-as-Code config file.

After discussions in HOSTING-875, this feature will put into the core plugin.

Your checklist for this pull request

🚨 Please review the guidelines for contributing to this repository.

• Make sure you are requesting to pull a topic/feature/bugfix branch (right side) and not your master branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or in Jenkins JIRA
• Link to relevant pull requests, esp. upstream and downstream changes
• Did you provide a test-case? That demonstrates feature works or fixes the issue.

[lgtm-com]

This pull request introduces 1 alert when merging 9b1ab63 into 0723f98 - view on LGTM.com

new alerts:

• 1 for Potential output resource leak