Implement support for self hosted GitLab in Release widget

### Description

would it be possible to support your own GitLab instance to see your projects on your homepage?

```
- type: releases
show-source-icon: true
collapse-after: 20
gitlab-url: git.YOURSERVER.dev
repositories:
- my/project
```

As far as I know GitLab CE and GitLab comercial are using the same way to access data. So it would just need a way to set the URL and no extra functionality.

I would really appreciate it.

Start by locating the Release widget and its GitLab data-access entry point. Trace how the current GitLab URL is configured and used, then identify the existing release-widget tests or checks. Done means the widget accepts a self-hosted GitLab URL and displays releases from the configured instance without breaking the default service.

Written by the indexing model from the issue text.