Use matching gitaly binary for workhorse integration tests

What does this MR do and why?

Extracted from !71047 (comment 698875719)

We have a workhorse integration test that pulls the latest Gitaly docker image and runs against the Gitaly server. At the moment, the version for such test is so outdated (13 months lagged behind). This MR is to bump that image version, and write some more integration tests for new PostUploadPackWithSidechannel RPC.

The image Dockerfile is available at https://gitlab.com/gitlab-org/build/CNG/-/tree/master/gitaly. The latest tag hasn't been updated for a while because the recent release CI job definition tags the images with master-ubi8 suffix. It looks like we migrated to use UBI8 image for a while. The new images were indeed smaller.

REPOSITORY                                                        TAG                                             IMAGE ID       CREATED         SIZE
registry.gitlab.com/gitlab-org/build/cng/gitaly                   2a077b03f578fefb1f24ac4e0a4cb68dbe10d1ae-ubi8   9cbafdc5498b   3 hours ago     979MB
registry.gitlab.com/gitlab-org/build/cng/gitaly                   master-ubi8                                     9cbafdc5498b   3 hours ago     979MB
registry.gitlab.com/gitlab-org/build/cng/gitaly                   latest                                          72764e236d08   13 months ago   1.97GB

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