Rewriting Git history to place all work in a subfolder instead of root
Solution 1:
git filter-branch --commit-filter '
toptree=`printf "040000 tree %s\\tserver" $1 | git mktree`
shift
git commit-tree $toptree "$@"
' -- --branches
Solution 2:
You are looking for git filter-repo. This is just the kind of thing it was written to do; see #3 in the rationale section of the readme.
https://github.com/newren/git-filter-repo#design-rationale-behind-filter-repo