Docs modifications (#5804)

- Fixes #5504
- Fixes #5503
- Return 404 when the page does not exist
- Modified the footer in order to align it properly
- Removed "noticed something to change" in each table of content
- Fixed the URLs of the edit module 
- Added the edit module to Developers
- Fixed header style on the REST API page.
- Edited the README to point to Developers
- Fixed selected state when clicking on sidebar elements

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Co-authored-by: Félix Malfait <felix.malfait@gmail.com>

packages/twenty-website/src/app/_components/docs/DocsSideBar.tsx

@@ -19,7 +19,6 @@ const StyledContainer = styled.div`
     flexDirection: 'column',
     background: `${Theme.background.secondary}`,
     borderRight: `1px solid ${Theme.background.transparent.medium}`,
-    borderBottom: `1px solid ${Theme.background.transparent.medium}`,
     padding: `${Theme.spacing(10)} ${Theme.spacing(4)}`,
     gap: `${Theme.spacing(6)}`,
   })}