Support xcode-version-badge-markdown-file option

Action will no longer push to existing branch when there are no changes

With WWDC 2021 just around the corner I've been thinking about what I'd like to see there.

A lot of the popular discourse around this time of year is focussed on features of the operating systems but I want to look at what I'd like to see as a developer for Apple platforms.

I love to develop for Apple platforms but it can often be a painful process. May is like a christmas for Apple developers.