Update links in documentation

[sashakames]

Hi, On https://www.esgf.io/esgf-prepare/configuration.html
there are several links to the old atlassian ESGF site. That is no longer maintained and problematic due to access control issues.

[zklaus]

I think the same applies to https://esgf.github.io/esgf-prepare/index.html, along with a broken link to a google doc document, which seems to describe the publication workflow.