Support publish_dir support for publishing a subdirectory to ghpages

[tusharjoshi]

gh-pages support a publish_dir parameter which is not available for this action, please provide support for that input parameter so a subdirectory of the branch can be published

I have a manual in subdirectory which needs the source code outside that folder to be included hence need to publish the manual/book folder from my branch after build.

https://github.com/tusharjoshi/design-patterns-workshop