Closes gitaly#921

Closes #42249

Given the priorities shifted for the Gitaly team, this endpoint does not
get a dedicated endpoint yet. To make it work in a cloud native
environment the request needs to go to Gitaly, not rugged. This is
achieved by rerouting to the generic TreeEntry endpoint.

This endpoint still has to be migrated, and this comment makes sure
everyone knows we are aware of this one.

[ci skip]

After installing a new gem, batch-loader, a construct can be used to
queue data to be fetched in bulk. The gem was also introduced in both
gitlab-org/gitlab-ce!14680 and gitlab-org/gitlab-ce!14846, but those mrs
are not merged yet.

For the generation of diffs, both the old blob and the new blob need to
be loaded. This for every file in the diff, too. Now we collect all
these so we do 1 fetch. Three `.allow_n_plus_1_calls` have been removed,
which I expect to be valid, but this needs to be confirmed by a full CI
run.

Possibly closes:
- https://gitlab.com/gitlab-org/gitlab-ce/issues/37445
- https://gitlab.com/gitlab-org/gitlab-ce/issues/37599
- https://gitlab.com/gitlab-org/gitlab-ce/issues/37431

Adds a rubocop rule (with autocorrect) to ensure line break after guard clauses.

Gitlab::Git::Blob.batch_lfs_metadata can be used to check for LFS pointers. It uses a lazy enumorator and filters by blob size

In gitlab-org/gitlab-ee!2976, we saw that a given OID could point
to a commit, which would cause the delta size check to fail.
Gitaly already returns nil if the OID isn't a blob, so this change
makes the Rugged implementation consistent.

remove some lint

An upcoming update to rubocop-gitlab-security added additional
violations.

Detect if file that appears to be text in the first 1024 bytes is actually binary afer loading all data

Use the EnforcedStyleForMultiline: no_comma option.

Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>