OGS-6: Test data files with git-lfs migration information

Dear all,

this email is of interest for OGS-6 developers only. Please ignore it otherwise.

We recently switched to git-lfs for storing (large or binary) test data files (benchmark and reference files). It requires some work on your end to migrate existing feature branches. See this PR for a description:

Git LFS for Tests/Data #1982

Previously these files were stored on GitHub but we encountered a download limit very fast and moved these files to our own GitLab server. See this PR:

Switch to GitLab for lfs #1984

Downloading (cloning / pulling) the new files should work out of box. If you want to push new files you need access to a ogs-repo on the GitLab server. See the documentation on how to login (please send me an email once done so I can unblock your account and give you access to the ogs group).

@ Karsten, Tom, Wenqing, Christoph and Dima: you already have accounts.

If you have problems please let me know.