What
---
1. Create a new home page for cell infrastructure.
2. Document philosophy for infrastructure.
3. Add new terms specifically for infrastructure.
4. Create an architecture diagram.
5. Identify large domains/unknowns, and dependencies between them.
6. Add Stakeholders
7. Reject the old deployment architecture

Video: https://youtu.be/AvTbIMVOuvY

Why
---
1. We do not have a single page for Cells infrastructure that links to
multiple areas of the infrastructure, making things hard to find.
2. Having a common philosophy on how we approach infrastructure will be
   helpful, and we can discuss fundamental disagreements.
3. Everyone is using these words differently, we've heard `deployment`
   being used for code changes and also provisioning the infrastructure.
4. We don't have a details architecture for what the infrastructure will look
   like.
6. Everyone has a part in this project so we need to identify who owns
   what. This originally lived in application deployment, but it makes
   more sense to move it to the index page.
5. We struggled to figure out which area we should focus on, creating a
   dependency chart will help with this.
7. This document was created before Cells 1.0 so things changed
   considerably.

Reference: #439562


Signed-off-by: Steve Xuereb <sxuereb@gitlab.com>