Add a loading page, and add to routing

[cherylli]

Task

• [ ] Add loading screen (e.g. when it takes 10s to load the frontpage because of network issues)
• [ ] add them to routing (client/src/app.js)

Suggested Method Example: https://github.com/chingu-voyages/v40-bears-team-37/blob/main/client/src/components/Loader/Loader.tsx https://github.com/chingu-voyages/v40-bears-team-37/blob/main/client/src/App.tsx

Feel free to use any (better) method

[cherylli]

Loading screen added but only to redirect at this stage #128