chore: update CI/CD configuration and dependencies

* Update `.gitlab-ci.yml` for new stages and rules.
* Change `TargetFramework` to `net9.0` in props file.
* Upgrade package references in `Api.csproj` to 9.x.
* Modify `Dockerfile` to use .NET 9.0 images.
* Add version endpoint in `Program.cs`.
* Update package references in `Application.csproj` to 9.x.
* Introduce `.releaserc.js` for semantic versioning.
* Add `.build_stage.yml` for emailsender build job.
* Implement secret detection in `.check_stage.yml`.
* Create `.docker_build_stage.yml` for Docker image builds.
* Add `.release_stage.yml` for managing releases.
* Comment out `.test_stage.yml` for now.