Add redis to contributor guide (#7369)

## Context

We are adding redis to default twenty configuration. 

## What

1. This PR sets up the local setup for contributors accordingly

2. I'm also updating the code blocks guide:

Before:
<img width="921" alt="image"
src="https://github.com/user-attachments/assets/2203cc99-b5a5-4d05-a8b1-98a348aee9df">


After:
<img width="921" alt="image"
src="https://github.com/user-attachments/assets/5b3e6f34-723d-4309-888b-c02ce794891d">

packages/twenty-website/src/app/layout.css

@@ -124,9 +124,3 @@ strong,
     font-weight: 500;
     text-decoration: none;
 }
-
-code {
-    background: #1414140a;
-    padding: 4px;
-    border-radius: 4px;
-  }