Gitaly's FetchIntoObjectPool RPC will idempotently fetch objects into an
object pool. If the pool doesn't exist, it will create an empty pool
before attempting the fetch. This change adds client code as well as
specs to cover this behavior.
If a diff happened to include a single null byte anywhere, insertion
into the database would fail with an Error 500 since the column is text
and not a byte array. To fix this, we mark the diff as binary if we
detect a single null byte and Base64-encode it.
Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/57710
Thong Kuah