Add option to only update the confluence document if the document is changed.

[danapsimer]

Is your feature request related to a problem? Please describe.
I have a large number of markdown files that I want to sync with my confluence space, however, I do not want the history to be cluttered with changes every time I execute my deployment script.

Describe the solution you'd like
I thought that if I could compare the document generated by mark and the current document in confluence. I have a branch in my fork with some code but it does not work because the HTML that mark is sending is not what we get back through using the "content/{id}" endpoint with "expand" including "body,body.storage". https://github.com/danapsimer/mark/tree/update-if-changed

Describe alternatives you've considered
I have another PR that does help this use case using an "upate-if-older-than" logic. See this PR: #489

Additional context

[frederikb]

As an alternative approach: a different tool which has a similar goal (publish Markdown to Confluence) uses a hash of the page contents + attachments and includes it in the version update message. This enables it to easily detect if the local copy has changes without needing to perform a diff with the actual remote contents.