builtin/upload-archive: fix leaking args passed to `write_archive()`

builtin/upload-archive: fix leaking args passed to `write_archive()`

In git-upload-archive(1), we pass an array of arguments to
`write_archive()` to tell it what exactly to do. We don't ever clear the
vector though, causing a memory leak. Furthermore though, the call to
`write_archive()` may cause contents of the array to be modified, which
would cause us to leak memory to allocated strings held by it.

Fix the issue by having `write_archive()` create a shallow copy of
`argv` before parsing the arguments. Like this, we won't modify the
caller's array and can easily `strvec_clear()` it to plug these memory
leaks.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>