1. Gitlab Github Bitbucket Integration

Yes, there are several online sites that can be connected to your GitHub, GitLab, or Bitbucket accounts and allow you to add files to your repositories after authorization. These sites generally use the APIs provided by these platforms to interact with your accounts.

Here are some examples of the types of sites and tools that offer this functionality:

2. Online code editors (Web IDEs) connected to Git repositories:

GitHub Codespaces: Integrated directly into GitHub, it offers a complete development environment in your browser, connected to your repository. You can edit, create, and add files directly.
GitLab Web IDE: Similar to Codespaces, it is integrated with GitLab and allows you to edit files in your repository directly in the web interface. StackBlitz: An online code editor that can connect to your GitHub repositories and allow you to create and add files.
CodeSandbox: Another online code editing platform that supports integration with GitHub and Bitbucket for adding and editing files.
3. Content Management System (CMS) or Static Site Tools with Git Integration:

Netlify CMS: An open-source, Git-based CMS that connects to your GitHub, GitLab, or Bitbucket repository. It allows users to add and edit content through a user-friendly interface, with changes then being committed and pushed to your repository.
Forestry.io (now TinaCMS Cloud): Another Git-based CMS that provides an interface for managing your static site content stored in a Git repository (GitHub, GitLab, Bitbucket). Changes are saved as commits in your repository. CloudCannon: A platform for managing static sites that connects to your Git repositories and provides a visual interface for editing and adding content, with changes synced to your repository.