fix(setup): add leading slash validation for baseUrl

[gauthier-th]

Description

Add a missing validation to ensure that the baseUrl starts with a slash.

Screenshot (if UI-related)

To-Dos

• [x] Successful build pnpm build
• [ ] Translation keys pnpm i18n:extract
• [ ] Database migration (if required)

[Fallenbagel]

:tada: This PR is included in version 2.1.0 :tada:

The release is available on:

• v2.1.0
• GitHub release

Your semantic-release bot :package::rocket: