refactor: Extract Invitation routes to InvitationController (no-changelog) (#7726)

This PR:

- Creates `InvitationController`
- Moves `POST /users` to `POST /invitations` and move related test to
`invitations.api.tests`
- Moves `POST /users/:id` to `POST /invitations/:id/accept` and move
related test to `invitations.api.tests`
- Adjusts FE to use new endpoints
- Moves all the invitation logic to the `UserService`

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Co-authored-by: कारतोफ्फेलस्क्रिप्ट™ <aditya@netroy.in>

packages/cli/test/unit/services/user.service.test.ts

@@ -6,12 +6,14 @@ import { User } from '@db/entities/User';
 import { UserRepository } from '@db/repositories/user.repository';
 import { UserService } from '@/services/user.service';
 import { mockInstance } from '../../shared/mocking';
+import { RoleService } from '@/services/role.service';
 
 describe('UserService', () => {
 	config.set('userManagement.jwtSecret', 'random-secret');
 
 	mockInstance(Logger);
 	const repository = mockInstance(UserRepository);
+	mockInstance(RoleService);
 	const service = Container.get(UserService);
 	const testUser = Object.assign(new User(), {
 		id: '1234',