Replace several links to gitlab.hzdr.de with codebase.helmholtz.cloud

.gitmodules

CONTRIBUTING.md

README.md

_config.yml

_events/2020/2020-05-12-ready-script-for-publication.md

...ts/2020/2020-11-12-bring-script-make-ready-publication.md

_posts/2019/11/2019-11-22-How-to-Create-a-new-Blog-Post.md

_posts/2019/12/2019-12-20-Welcome-Post.md

_posts/2020/01/2020-01-07-contributing-in-4-simple-steps.md

_posts/2020/04/2020-04-15-smime-signing-git-commits.md

_posts/2020/04/2020-04-17-online-swc-at-hzdr.md

_posts/2020/09/2020-09-16-hifis-homepage-helpdesk.md

_posts/2021/01/2021-01-26-1000-users.md

_posts/2021/02/2021-02-09-helmholtz-gitlab.md

_posts/2021/03/2021-03-23-helmholtz-aai-in-dfn-meeting.md

_posts/2021/06/2021-06-02-easy-diagram-creation-in-gitlab.md

_posts/2021/08/2021-08-20-support-punch4nfdi.md

_posts/2021/10/2021-10-20-use-case-hts.md

...1-10-22-helmholtz-aai-full-presentation-in-dfn-meeting.md

_posts/2021/12/2021-12-20-survey-report.md