feat(custom-domains): allow to register a custom domain (without UI) (#9879)

# In this PR
- Allow to register a custom domain
- Refacto subdomain generation

# In other PRs
- Add UI to deal with a custom domain
- Add logic to work with custom domain

packages/twenty-front/src/modules/users/graphql/fragments/userQueryFragment.ts

@@ -37,6 +37,7 @@ export const USER_QUERY_FRAGMENT = gql`
       isPasswordAuthEnabled
       subdomain
       hasValidEnterpriseKey
+      hostname
       featureFlags {
         id
         key