Use batched new blobs check [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

The Git access checks support checking the size of pushed objects. If we have a quarantine environment (which is always the case when access checks are executed via git receive-pack's hooks), then we simply derive the size from the quarantined objects. Otherwise, we use get_new_blobs, which does a git rev-list $REVISION --not --all.

Using git-rev-list(1) with --not --all can be a very expensive operation depending on the repository's shape. Especially when it's a biggish monorepo with lots of references, this query can easily take tens of seconds. Given that we call the RPC once per change, this thus roughly scales O(len(changes) * len(existing_refs)).

To improve this situation, Gitaly has implemented a new list_blobs() RPC which takes a set of revisions. Like this, we can batch all calls into a single one and thus avoid some of the overhead if there are multiple changes at once. The new code which does that is currently implemented behind a feature flag.

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team