Modified URLs and added button to share on LinkedIn (#5306)

- Removed the env variable and added the current URL in contributor's
page
- Added button to share on LinkedIn on contributor's profile
- Fixed absolute image URL for release API

---------

Co-authored-by: Ady Beraud <a.beraud96@gmail.com>

packages/twenty-website/.env.example

@@ -1,4 +1,2 @@
 GITHUB_TOKEN=your_github_token
 DATABASE_PG_URL=postgres://website:website@localhost:5432/website # only if using postgres
-NEXT_PUBLIC_HOST_URL=http://localhost:3000
-