Add gh service

[sridamul]

Added GH service class which allows us to fork and clone plugin, commit the changes (after transformation) and PR creation.

Note: GH token and username is passed through system env variables.

This is a rough PR, open to improvements. Thanks!

Testing done

This PR is automated with the tool starting from forking, cloning and PR creation

Log file

Starting Plugin Modernizer 
Plugins: [login-theme-plugin] 
Recipes: [AddPluginsBom] 
Forking and cloning login-theme-plugin locally 
Forking the repository... 
Repository forked successfully 
Cloning login-theme-plugin 
Cloned successfully 
Invoking clean phase for plugin: login-theme-plugin 
Invoking rewrite plugin for plugin: login-theme-plugin 
Creating pull request for plugin: login-theme-plugin 
Changes committed 
Pushed changes to forked repository 
Pull request created: https://github.com/sridamul/login-theme-plugin/pull/8 

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

[jonesbusy]

Some minor code issues/improvement and I think we can do ahead with this first integration with JGit/GitHub

Also don't forget to document on the README.md the new parameter of needed environment variables

[sridamul]

Tested manually with dry run option.

[jonesbusy]

Can you please track an issue to ensure the GH repo is in sync with upstream. It should be possible via API

I'm using generally the gh repo sync username/repo

Without sync existing repo there is a risk to open branches from outdated main branch