feat: archive

This implements a subset of git-archive. I've tested with files (including symlinks and executables) and folders:

$ git --git-dir=$HOME/Sandbox/repo/.git archive --format=tar HEAD | tar -tvf -
-rw-rw-r-- root/root        10 2024-05-13 16:42 a.txt
drwxrwxr-x root/root         0 2024-05-13 16:42 b/
-rw-rw-r-- root/root        21 2024-05-13 16:42 b/b1.txt
-rwxrwxr-x root/root        23 2024-05-13 16:42 c.sh
lrwxrwxrwx root/root         0 2024-05-13 16:42 root_b1.txt -> b/b1.txt

$ bazel run -- cmd/bazel-git --git-dir=$HOME/Sandbox/repo/.git archive --format=tar HEAD 2> /dev/null | tar -tvf -
-rw-r--r-- 0/0              10 2024-05-13 16:42 a.txt
drwxrwxr-x 0/0               0 2024-05-13 16:42 b/
-rw-r--r-- 0/0              21 2024-05-13 16:42 b/b1.txt
-rwxr-xr-x 0/0              23 2024-05-13 16:42 c.sh
lrwxrwxrwx 0/0               0 2024-05-13 16:42 root_b1.txt -> b/b1.txt

There are a few differences in terms of permissions, but that shouldn't matter.