Is there a way to auto-add a newly installed plugin as a dependency, so I can later run gpm/install on a server? Something like npm does with “npm install --save package-name”?
Hi, i aksed myself the same question some days ago. On Github there is already an issue to this #880. Thanks to Perlkönig for the link 
You can also manually build a .dependencies file like you would when building a skeleton.
I already have the file after installing grav through git. Problem is, every time I add a plugin, I need to manually update .dependencies file. This is because I chose to not include plugins in my git repo, so I can just run bin/grav install on the server after updating from git. For this, I need the file to always contain all installed plugins.
I understand. Thus the issue #880 to create a freeze/thaw function. I was just saying that you could do it manually in the meantime.