fetch-pack: expose fsckObjects configuration logic

fetch-pack: expose fsckObjects configuration logic

Currently, we can use "transfer.fsckObjects" and the more specific
"fetch.fsckObjects" to control checks for broken objects in received
packs during fetches. However, these configurations were only
acknowledged by `fetch-pack.c:get_pack` and did not take effect in
direct bundle fetches or fetches with _bundle-uri_ enabled.

This commit exposes the fetch-then-transfer configuration logic by
adding a new function `fetch_pack_fsck_objects` in fetch-pack.h. This
new function is used to replace the assignment for `fsck_objects` in
`fetch-pack.c:get_pack`. In the next commit, this function will also be
used to extend fsck support for bundle-involved fetches.

Helped-by: Junio C Hamano <gitster@pobox.com>
Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Xing Xin <xingxin.xx@bytedance.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>