New Diffs: Document current implementation of Diffs across GitLab
# Context
In the context of the New Diffs effort ([Epic](https://gitlab.com/groups/gitlab-org/-/epics/11559)), we aim to use this issue to collaborate documenting the current implementation of Diffs.
# Scope
Implementations to document:
* Repository Commit
* Compare Branches
* Merge Requests (Changes)
* New Merge Request form
* ...?
Note: We'll need to document how data flows from gitaly to rails to caching to frontend.
# How?
We should keep it somewhat simple but perhaps a mermaid chart with a blurb of text explaining details could suffice at this point? Open for discussion and other proposals.
<details><summary><b>Example</b> (really rough, please improve)</summary>
```mermaid
flowchart TD
subgraph "repository_commits"
rails_repo["Repository Rails"]
db_repo["Repository DB"]
cache_repo["Redis"]
fe_repo["Frontend (HAML)"]
end
subgraph "gitaly"
end
gitaly --> rails_repo
rails_repo --> db_repo
rails_repo --> cache_repo
cache_repo --> rails_repo
rails_repo --> fe_repo
```
</details>
issue