Add state mover for gitlab_project_integration_jenkins

This code change adds support for migrating from an old Jenkins integration resource (gitlab_integration_jenkins) to a new one (gitlab_project_integration_jenkins) in a Terraform provider for GitLab.

The main addition is a "state mover" function that automatically transfers configuration data when users upgrade from the deprecated resource to the new one using Terraform's moved block feature. This migration capability includes validation checks to ensure it only moves data from the correct source resource and provider.

The code also adds a comprehensive test to verify the migration works properly - it creates a Jenkins integration using the old resource, moves it to the new resource, and confirms everything still functions correctly after the move.

This change helps users smoothly transition from the old resource to the new one without losing their existing configuration or having to manually recreate their Jenkins integrations.

Part of #6717