[Meta] Common tasks for LFS pruning / integrity

What

This is a meta issue regarding progress on https://gitlab.com/gitlab-org/gitlab-ce/issues/30639 and https://gitlab.com/gitlab-org/gitlab-ce/issues/24564, as worked in in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14479, https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13837 and https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14785

Why

This issue provides central place for updates while I switch between working on the two. They both currently share use of rev-list and blob lookup which need performance to be verified.

Todo

• Rev-list memory benchmark on large project such as linux repo
• Combined new_objects memory check when using rev-list along with blob lookup
• Pruning MR todos (https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14479#todo) and review comments
• Merge https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14785
• Merge pruning / garbage collection MR
• Integrity review comments and todos
• Merge integrity / push prevention MR